This paper aims to share the author's vision on possible research directions for big knowledge-based AI. A renewed definition of big knowledge (BK) and big knowledge systems (BKS) is first introduced. Then the first BKS model, called cloud knowledge social intelligence (CKEI) is provided with a hierarchy of knowledge as a service (KAAS). At last, a new semantics, the big-and-broad step axiomatic structural operational semantics (BBASOS) for applications on BKS is introduced and discussed with a practical distributed BKS model knowledge graph network KGN and a mini example.

November 19-22, 2013 Alexander Technological Educational Institute of Thessaloniki, Greece

Continuing the successful mission of previous MTSR Conferences (MTSR'05, MTSR'07, MTSR'09, MTSR'10, MTSR'11 and MTSR’12), the seventh International Conference on Metadata and Semantics Research (MTSR'13) aims to bring together scholars and practitioners that share a common interest in the interdisciplinary field of metadata, linked data and ontologies. Participants will share novel knowledge and best practice in the implementation of these semantic technologies across diverse types of Information Environments and applications. These include Cultural Informatics; Open Access Repositories & Digital Libraries; E-learning applications; Search Engine Optimisation & Information Retrieval; Research Information Systems and Infrastructures; e-Science and e-Social Science applications; Agriculture, Food and Environment; Bio-Health & Medical Information Systems.

The ESWC 2013 takes place from May 26th, 2013 to May 30th, 2013 in Montpellier, France.
The ESWC is a major venue for discussing the latest scientific results and technology innovations around semantic technologies. Building on its past success, ESWC is seeking to broaden its focus to span other relevant research areas in which Web semantics plays an important role.
Event web site: ESWC 2013

Continuing the successful mission of previous MTSR Conferences (MTSR'05, MTSR'07, MTSR'09, MTSR'10, MTSR'11 and MTSR’12), the seventh International Conference on Metadata and Semantics Research (MTSR'13) aims to bring together scholars and practitioners that share a common interest in the interdisciplinary field of metadata, linked data and ontologies. Participants will share novel knowledge and best practice in the implementation of these semantic technologies across diverse types of Information Environments and applications. These include Cultural Informatics; Open Access Repositories & Digital Libraries; E-learning applications; Search Engine Optimisation & Information Retrieval; Research Information Systems and Infrastructures; e-Science and e-Social Science applications; Agriculture, Food and Environment; Bio-Health & Medical Information Systems. 

ETSI IoT Week: semantics, experiences and security

Sophia Antipolis, 28 October 2019

ETSI IoT Week 2019 (21-25 October) drew more than 200 attendees to ETSI’s headquarters for what has become a must attend event for anyone who wants to understand the importance of standard-enabled technologies for IoT service deployments, in many different sectors.

Read More...

YSTR-DG.SEM - oneM2M-Developer Guide of Implementing semantics

Specification and Description Language - Overview of SDL-2010 - SDL-2010 formal definition: Dynamic semantics

Specification and Description Language - Overview of SDL-2010 - SDL-2010 formal definition: Static semantics

Specification and Description Language - Overview of SDL-2010 - SDL formal definition: Dynamic semantics

Specification and Description Language - Overview of SDL-2010 - SDL formal definition: Static semantics

Interaction languages such as MSC are often associated with formal semantics by means of translations into distinct behavioral formalisms such as automatas or Petri nets. In contrast to translational approaches we propose an operational approach. Its principle is to identify which elementary communication actions can be immediately executed, and then to compute, for every such action, a new interaction representing the possible continuations to its execution. We also define an algorithm for checking the validity of execution traces (i.e. whether or not they belong to an interaction's semantics). Algorithms for semantic computation and trace validity are analyzed by means of experiments.

We develop a categorical compositional distributional semantics for Lambek Calculus with a Relevant Modality !L*, which has a limited edition of the contraction and permutation rules. The categorical part of the semantics is a monoidal biclosed category with a coalgebra modality, very similar to the structure of a Differential Category. We instantiate this category to finite dimensional vector spaces and linear maps via "quantisation" functors and work with three concrete interpretations of the coalgebra modality. We apply the model to construct categorical and concrete semantic interpretations for the motivating example of !L*: the derivation of a phrase with a parasitic gap. The effectiveness of the concrete interpretations are evaluated via a disambiguation task, on an extension of a sentence disambiguation dataset to parasitic gap phrase one, using BERT, Word2Vec, and FastText vectors and Relational tensors.

Intended meaning. In computing, semantics is the assumed or explicit set of understandings used in a system to give meaning to data. One of the biggest challenges when integrating separate computer systems and applications is to correctly match up the intended meanings within each system. Simple metadata classifications such as 'price' or 'location' may have wildly different meanings in each system, while apparently different terms, such as 'client' and 'patient' may turn out to be effectively equivalent.

Cham : Springer, 2019.

Oxford : Oxford University Press, 2020.

As a child of the ’90s, one of my favorite movie quotes is from Harriet the Spy: “there are as many ways to live as there are people in this world, and each one deserves a closer look.” Likewise, there are as many ways to browse the web as there are people online. We each bring unique context to our web experience based on our values, technologies, environments, minds, and bodies. Assistive technologies (ATs), which are hardware and software that help us perceive and interact with digital content, come in diverse forms. ATs can use a whole host of user input, ranging from clicks and keystrokes to minor muscle movements. ATs may also present digital content in a variety of forms, such as Braille displays, color-shifted views, and decluttered user interfaces (UIs). One more commonly known type of AT is the screen reader. Programs such as JAWS, Narrator, NVDA, and VoiceOver can take digital content and present it to users through voice output, may display this output visually on the user’s screen, and can have Braille display and/or screen magnification capabilities built in. If you make websites, you may have tested your sites with a screen reader. But how do these and other assistive programs actually access your content? What information do they use? We’ll take a detailed step-by-step view of how the process works. (For simplicity we’ll continue to reference “browsers” and “screen readers” throughout this article. These are essentially shorthands for “browsers and other applications,” and “screen readers and other assistive technologies,” respectively.)

The semantics-to-screen-readers pipeline

Accessibility application programming interfaces (APIs) create a useful link between user applications and the assistive technologies that wish to interact with them. Accessibility APIs facilitate communicating accessibility information about user interfaces (UIs) to the ATs. The API expects information to be structured in a certain way, so that whether a button is properly marked up in web content or is sitting inside a native app taskbar, a button is a button is a button as far as ATs are concerned. That said, screen readers and other ATs can do some app-specific handling if they wish. On the web specifically, there are some browser and screen reader combinations where accessibility API information is supplemented by access to DOM structures. For this article, we’ll focus specifically on accessibility APIs as a link between web content and the screen reader. Here’s the breakdown of how web content reaches screen readers via accessibility APIs: The web developer uses host language markup (HTML, SVG, etc.), and potentially roles, states, and properties from the ARIA suite where needed to provide the semantics of their content. Semantic markup communicates what type an element is, what content it contains, what state it’s in, etc. The browser rendering engine (alternatively referred to as a “user agent”) takes this information and maps it into an accessibility API. Different accessibility APIs are available on different operating systems, so a browser that is available on multiple platforms should support multiple accessibility APIs. Accessibility API mappings are maintained on a lower level than web platform APIs, so web developers don’t directly interact with accessibility APIs. The accessibility API includes a collection of interfaces that browsers and other apps can plumb into, and generally acts as an intermediary between the browser and the screen reader. Accessibility APIs provide interfaces for representing the structure, relationships, semantics, and state of digital content, as well as means to surface dynamic changes to said content. Accessibility APIs also allow screen readers to retrieve and interact with content via the API. Again, web developers don’t interact with these APIs directly; the rendering engine handles translating web content into information useful to accessibility APIs.

Examples of accessibility APIs

• Windows: Microsoft Active Accessibility (MSAA), extended with another API called IAccessible2 (IA2)
• Windows: UI Automation (UIA), the Microsoft successor to MSAA. A browser on Windows can choose to support MSAA with IA2, UIA, or both.
• MacOS: NSAccessibility (AXAPI)
• Linux/Gnome: Accessibility Toolkit (ATK) and Assistive Technology Service Provider Interface (AT-SPI). This case is a little different in that there are actually two separate APIs: one through which browsers and other applications pass information along to (ATK) and one that ATs then call from (AT-SPI).

The screen reader uses client-side methods from these accessibility APIs to retrieve and handle information exposed by the browser. In browsers where direct access to the Document Object Model (DOM) is permitted, some screen readers may also take additional information from the DOM tree. A screen reader can also interact with apps that use differing accessibility APIs. No matter where they get their information, screen readers can dream up any interaction modes they want to provide to their users (I’ve provided links to screen reader commands at the end of this article). Testing by site creators can help identify content that feels awkward in a particular navigation mode, such as multiple links with the same text (“Learn more”), as one example.

Example of this pipeline: surfacing a button element to screen reader users

Let’s suppose for a moment that a screen reader wants to understand what object is next in the accessibility tree (which I’ll explain further in the next section), so it can surface that object to the user as they navigate to it. The flow will go a little something like this:

1. The screen reader requests information from the API about the next accessible object, relative to the current object.
2. The API (as an intermediary) passes along this request to the browser.
3. At some point, the browser references DOM and style information, and discovers that the relevant element is a non-hidden button: <button>Do a thing</button>.
4. The browser maps this HTML button into the format the API expects, such as an accessible object with various properties: Name: Do a thing, Role: Button.
5. The API returns this information from the browser to the screen reader.
6. The screen reader can then surface this object to the user, perhaps stating “Button, Do a thing.”

Suppose that the screen reader user would now like to “click” this button. Here’s how their action flows all the way back to web content:

1. The user provides a particular screen reader command, such as a keystroke or gesture.
2. The screen reader calls a method into the API to invoke the button.
3. The API forwards this interaction to the browser.
4. How a browser may respond to incoming interactions depends on the context, but in this case the browser can raise this as a “click” event through web APIs. The browser should give no indication that the click came from an assistive technology, as doing so would violate the user’s right to privacy.
5. The web developer has registered a JavaScript event listener for clicks; their callback function is now executed as if the user clicked with a mouse.

Now that we have a general sense of the pipeline, let’s go into a little more detail on the accessibility tree.

The accessibility tree

The accessibility tree is a hierarchical representation of elements in a UI or document, as computed for an accessibility API. In modern browsers, the accessibility tree for a given document is a separate, parallel structure to the DOM tree. “Parallel” does not necessarily mean there is a 1:1 match between the nodes of these two trees. Some elements may be excluded from the accessibility tree, for example if they are hidden or are not semantically useful (think non-focusable wrapper divs without any semantics added by a web developer). This idea of a hierarchical structure is somewhat of an abstraction. The definition of what exactly an accessibility tree is in practice has been debated and partially defined in multiple places, so implementations may differ in various ways. For example, it’s not actually necessary to generate accessible objects for every element in the DOM whenever the DOM tree is constructed. As a performance consideration, a browser could choose to deal with only a subset of objects and their relationships at a time—that is, however much is necessary to fulfill the requests coming from ATs. The rendering engine could make these computations during all user sessions, or only do so when assistive technologies are actively running. Generally speaking, modern web browsers wait until after style computation to build up any accessible objects. Browsers wait in part because generated content (such as ::before and ::after) can contain text that can participate in calculation of the accessible object’s name. CSS styles can also impact accessible objects in other various ways: text styling can come through as attributes on accessible text ranges. Display property values can impact the computation of line text ranges. These are just a few ways in which style can impact accessibility semantics. Browsers may also use different structures as the basis for accessible object computation. One rendering engine may walk the DOM tree and cross-reference style computations to build up parallel tree structures; another engine may use only the nodes that are available in a style tree in order to build up their accessibility tree. User agent participants in the standards community are currently thinking through how we can better document our implementation details, and whether it might make sense to standardize more of these details further down the road. Let’s now focus on the branches of this tree, and explore how individual accessibility objects are computed.

Building up accessible objects

From API to API, an accessible object will generally include a few things:

• Role, or the type of accessible object (for example, Button). The role tells a user how they can expect to interact with the control. It is typically presented when screen reader focus moves onto the accessible object, and it can be used to provide various other functionalities, such as skipping around content via one type of object.
• Name, if specified. The name is an (ideally short) identifier that better helps the user identify and understand the purpose of an accessible object. The name is often presented when screen focus moves to the object (more on this later), can be used as an identifier when presenting a list of available objects, and can be used as a hook for functionalities such as voice commands.
• Description and/or help text, if specified. We’ll use “Description” as a shorthand. The Description can be considered supplemental to the Name; it’s not the main identifier but can provide further information about the accessible object. Sometimes this is presented when moving focus to the accessible object, sometimes not; this variation depends on both the screen reader’s user experience design and the user’s chosen verbosity settings.
• Properties and methods surfacing additional semantics. For simplicity’s sake, we won’t go through all of these. For your awareness, properties can include details like layout information or available interactions (such as invoking the element or modifying its value).

Let’s walk through an example using markup for a simple mood tracker. We’ll use simplified property names and values, because these can differ between accessibility APIs.

<form>
  <label for="mood">On a scale of 1–10, what is your mood today?</label>
  <input id="mood" type="range"
       min="1" max="10" value="5"
       aria-describedby="helperText" />
  <p id="helperText">Some helpful pointers about how to rate your mood.</p>
  <!-- Using a div with button role for the purposes of showing how the accessibility tree is created. Please use the button element! -->
  <div tabindex="0" role="button">Log Mood</div>
</form>

First up is our form element. This form doesn’t have any attributes that would give it an accessible Name, and a form landmark without a Name isn’t very useful when jumping between landmarks. Therefore, HTML mapping standards specify that it should be mapped as a group. Here’s the beginning of our tree:

• Role: Group

Next up is the label. This one doesn’t have an accessible Name either, so we’ll just nest it as an object of role “Label” underneath the form:

• Role: Group
  • Role: Label

Let’s add the range input, which will map into various APIs as a “Slider.” Due to the relationship created by the for attribute on the label and id attribute on the input, this slider will take its Name from the label contents. The aria-describedby attribute is another id reference and points to a paragraph with some text content, which will be used for the slider’s Description. The slider object’s properties will also store “labelledby” and “describedby” relationships pointing to these other elements. And it will specify the current, minimum, and maximum values of the slider. If one of these range values were not available, ARIA standards specify what should be the default value. Our updated tree:

• Role: Group
  • Role: Label
  • Role: Slider Name: On a scale of 1–10, what is your mood today? Description: Some helpful pointers about how to rate your mood. LabelledBy: [label object] DescribedBy: helperText ValueNow: 5 ValueMin: 1 ValueMax: 10

The paragraph will be added as a simple paragraph object (“Text” or “Group” in some APIs):

• Role: Group
  • Role: Label
  • Role: Slider Name: On a scale of 1–10, what is your mood today? Description: Some helpful pointers about how to rate your mood. LabelledBy: [label object] DescribedBy: helperText ValueNow: 5 ValueMin: 1 ValueMax: 10
  • Role: Paragraph

The final element is an example of when role semantics are added via the ARIA role attribute. This div will map as a Button with the name “Log Mood,” as buttons can take their name from their children. This button will also be surfaced as “invokable” to screen readers and other ATs; special types of buttons could provide expand/collapse functionality (buttons with the aria-expanded attribute), or toggle functionality (buttons with the aria-pressed attribute). Here’s our tree now:

• Role: Group
  • Role: Label
  • Role: Slider Name: On a scale of 1–10, what is your mood today? Description: Some helpful pointers about how to rate your mood. LabelledBy: [label object] DescribedBy: helperText ValueNow: 5 ValueMin: 1 ValueMax: 10
  • Role: Paragraph
  • Role: Button Name: Log Mood

On choosing host language semantics

Our sample markup mentions that it is preferred to use the HTML-native button element rather than a div with a role of “button.” Our buttonified div can be operated as a button via accessibility APIs, as the ARIA attribute is doing what it should—conveying semantics. But there’s a lot you can get for free when you choose native elements. In the case of button, that includes focus handling, user input handling, form submission, and basic styling. Aaron Gustafson has what he refers to as an “exhaustive treatise” on buttons in particular, but generally speaking it’s great to let the web platform do the heavy lifting of semantics and interaction for us when we can. ARIA roles, states, and properties are still a great tool to have in your toolbelt. Some good use cases for these are

• providing further semantics and relationships that are not naturally expressed in the host language;
• supplementing semantics in markup we perhaps don’t have complete control over;
• patching potential cross-browser inconsistencies;
• and making custom elements perceivable and operable to users of assistive technologies.

Notes on inclusion or exclusion in the tree

Standards define some rules around when user agents should exclude elements from the accessibility tree. Excluded elements can include those hidden by CSS, or the aria-hidden or hidden attributes; their children would be excluded as well. Children of particular roles (like checkbox) can also be excluded from the tree, unless they meet special exceptions. The full rules can be found in the “Accessibility Tree” section of the ARIA specification. That being said, there are still some differences between implementers, some of which include more divs and spans in the tree than others do.

Notes on name and description computation

How names and descriptions are computed can be a bit confusing. Some elements have special rules, and some ARIA roles allow name computation from the element’s contents, whereas others do not. Name and description computation could probably be its own article, so we won’t get into all the details here (refer to “Further reading and resources” for some links). Some short pointers:

• aria-label, aria-labelledby, and aria-describedby take precedence over other means of calculating name and description.
• If you expect a particular HTML attribute to be used for the name, check the name computation rules for HTML elements. In your scenario, it may be used for the full description instead.
• Generated content (::before and ::after) can participate in the accessible name when said name is taken from the element’s contents. That being said, web developers should not rely on pseudo-elements for non-decorative content, as this content could be lost when a stylesheet fails to load or user styles are applied to the page.

When in doubt, reach out to the community! Tag questions on social media with “#accessibility.” “#a11y” is a common shorthand; the “11” stands for “11 middle letters in the word ‘accessibility.’” If you find an inconsistency in a particular browser, file a bug! Bug tracker links are provided in “Further reading and resources.”

Not just accessible objects

Besides a hierarchical structure of objects, accessibility APIs also offer interfaces that allow ATs to interact with text. ATs can retrieve content text ranges, text selections, and a variety of text attributes that they can build experiences on top of. For example, if someone writes an email and uses color alone to highlight their added comments, the person reading the email could increase the verbosity of speech output in their screen reader to know when they’re encountering phrases with that styling. However, it would be better for the email author to include very brief text labels in this scenario. The big takeaway here for web developers is to keep in mind that the accessible name of an element may not always be surfaced in every navigation mode in every screen reader. So if your aria-label text isn’t being read out in a particular mode, the screen reader may be primarily using text interfaces and only conditionally stopping on objects. It may be worth your while to consider using text content—even if visually hidden—instead of text via an ARIA attribute. Read more thoughts on aria-label and aria-labelledby.

Accessibility API events

It is the responsibility of browsers to surface changes to content, structure, and user input. Browsers do this by sending the accessibility API notifications about various events, which screen readers can subscribe to; again, for performance reasons, browsers could choose to send notifications only when ATs are active. Let’s suppose that a screen reader wants to surface changes to a live region (an element with role="alert" or aria-live):

1. The screen reader subscribes to event notifications; it could subscribe to notifications of all types, or just certain types as categorized by the accessibility API. Let’s assume in our example that the screen reader is at least listening to live region change events.
2. In the web content, the web developer changes the text content of a live region.
3. The browser (provider) recognizes this as a live region change event, and sends the accessibility API a notification.
4. The API passes this notification along to the screen reader.
5. The screen reader can then use metadata from the notification to look up the relevant accessible objects via the accessibility API, and can surface the changes to the user.

ATs aren’t required to do anything with the information they retrieve. This can make it a bit trickier as a web developer to figure out why a screen reader isn’t announcing a change: it may be that notifications aren’t being raised (for example, because a browser is not sending notifications for a live region dynamically inserted into web content), or the AT is not subscribed or responding to that type of event.

Testing with screen readers and dev tools

While conformance checkers can help catch some basic accessibility issues, it’s ideal to walk through your content manually using a variety of contexts, such as

• using a keyboard only;
• with various OS accessibility settings turned on;
• and at different zoom levels and text sizes, and so on.

As you do this, keep in mind the Web Content Accessibility Guidelines (WCAG 2.1), which give general guidelines around expectations for inclusive web content. If you can test with users after your own manual test passes, all the better! Robust accessibility testing could probably be its own series of articles. In this one, we’ll go over some tips for testing with screen readers, and catching accessibility errors as they are mapped into the accessibility API in a more general sense.

Screen reader testing

Screen readers exist in many forms: some are pre-installed on the operating system and others are separate applications that in some cases are free to download. The WebAIM screen reader user survey provides a list of commonly used screen reader and browser combinations among survey participants. The “Further reading and resources” section at the end of this article includes full screen reader user docs, and Deque University has a great set of screen reader command cheat sheets that you can refer to. Some actions you might take to test your content:

• Read the next/previous item.
• Read the next/previous line.
• Read continuously from a particular point.
• Jump by headings, landmarks, and links.
• Tab around focusable elements only.
• Get a summary of all elements of a particular type within the page.
• Search the page for specific content.
• Use table-specific commands to interact with your tables.
• Jump around by form field; are field instructions discoverable in this navigational mode?
• Use keyboard commands to interact with all interactive elements. Are your JavaScript-driven interactions still operable with screen readers (which can intercept key input in certain modes)? WAI-ARIA Authoring Practices 1.1 includes notes on expected keyboard interactions for various widgets.
• Try out anything that creates a content change or results in navigating elsewhere. Would it be obvious, via screen reader output, that a change occurred?

Tracking down the source of unexpected behavior

If a screen reader does not announce something as you’d expect, here are a few different checks you can run:

• Does this reproduce with the same screen reader in multiple browsers on this OS? It may be an issue with the screen reader or your expectation may not match the screen reader’s user experience design. For example, a screen reader may choose to not expose the accessible name of a static, non-interactive element. Checking the user docs or filing a screen reader issue with a simple test case would be a great place to start.
• Does this reproduce with multiple screen readers in the same browser, but not in other browsers on this OS? The browser in question may have an issue, there may be compatibility differences between browsers (such as a browser doing extra helpful but non-standard computations), or a screen reader’s support for a specific accessibility API may vary. Filing a browser issue with a simple test case would be a great place to start; if it’s not a browser bug, the developer can route it to the right place or make a code suggestion.
• Does this reproduce with multiple screen readers in multiple browsers? There may be something you can adjust in your code, or your expectations may differ from standards and common practices.
• How does this element’s accessibility properties and structure show up in browser dev tools?

Inspecting accessibility trees and properties in dev tools

Major modern browsers provide dev tools to help you observe the structure of the accessibility tree as well as a given element’s accessibility properties. By observing which accessible objects are generated for your elements and which properties are exposed on a given element, you may be able to pinpoint issues that are occurring either in front-end code or in how the browser is mapping your content into the accessibility API. Let’s suppose that we are testing this piece of code in Microsoft Edge with a screen reader:

<div class="form-row">
  <label>Favorite color</label>
  <input id="myTextInput" type="text" />
</div>

We’re navigating the page by form field, and when we land on this text field, the screen reader just tells us this is an “edit” control—it doesn’t mention a name for this element. Let’s check the tools for the element’s accessible name. 1. Inspect the element to bring up the dev tools.

2. Bring up the accessibility tree for this page by clicking the accessibility tree button (a circle with two arrows) or pressing Ctrl+Shift+A (Windows).

Reviewing the accessibility tree is an extra step for this particular flow but can be helpful to do. When the Accessibility Tree pane comes up, we notice there’s a tree node that just says “textbox:,” with nothing after the colon. That suggests there’s not a name for this element. (Also notice that the div around our form input didn’t make it into the accessibility tree; it was not semantically useful). 3. Open the Accessibility Properties pane, which is a sibling of the Styles pane. If we scroll down to the Name property—aha! It’s blank. No name is provided to the accessibility API. (Side note: some other accessibility properties are filtered out of this list by default; toggle the filter button—which looks like a funnel—in the pane to get the full list).

4. Check the code. We realize that we didn’t associate the label with the text field; that is one strategy for providing an accessible name for a text input. We add for="myTextInput" to the label:

<div class="form-row">
  <label for="myTextInput">Favorite color</label>
  <input id="myTextInput" type="text" />
</div>

And now the field has a name:

In another use case, we have a breadcrumb component, where the current page link is marked with aria-current="page":

<nav class="breadcrumb" aria-label="Breadcrumb">
  <ol>
    <li>
      <a href="/cat/">Category</a>
    </li>
    <li>
      <a href="/cat/sub/">Sub-Category</a>
    </li>
    <li>
      <a aria-current="page" href="/cat/sub/page/">Page</a>
    </li>
  </ol>
</nav>

When navigating onto the current page link, however, we don’t get any indication that this is the current page. We’re not exactly sure how this maps into accessibility properties, so we can reference a specification like Core Accessibility API Mappings 1.2 (Core-AAM). Under the “State and Property Mapping” table, we find mappings for “aria-current with non-false allowed value.” We can check for these listed properties in the Accessibility Properties pane. Microsoft Edge, at the time of writing, maps into UIA (UI Automation), so when we check AriaProperties, we find that yes, “current=page” is included within this property value.

Now we know that the value is presented correctly to the accessibility API, but the particular screen reader is not using the information. As a side note, Microsoft Edge’s current dev tools expose these accessibility API properties quite literally. Other browsers’ dev tools may simplify property names and values to make them easier to read, particularly if they support more than one accessibility API. The important bit is to find if there’s a property with roughly the name you expect and whether its value is what you expect. You can also use this method of checking through the property names and values if mapping specs, like Core-AAM, are a bit intimidating!

Advanced accessibility tools

While browser dev tools can tell us a lot about the accessibility semantics of our markup, they don’t generally include representations of text ranges or event notifications. On Windows, the Windows SDK includes advanced tools that can help debug these parts of MSAA or UIA mappings: Inspect and AccEvent (Accessible Event Watcher). Using these tools presumes knowledge of the Windows accessibility APIs, so if this is too granular for you and you’re stuck on an issue, please reach out to the relevant browser team! There is also an Accessibility Inspector in Xcode on MacOS, with which you can inspect web content in Safari. This tool can be accessed by going to Xcode > Open Developer Tool > Accessibility Inspector.

Diversity of experience

Equipped with an accessibility tree, detailed object information, event notifications, and methods for interacting with accessible objects, screen readers can craft a browsing experience tailored to their audiences. In this article, we’ve used the term “screen readers” as a proxy for a whole host of tools that may use accessibility APIs to provide the best user experience possible. Assistive technologies can use the APIs to augment presentation or support varying types of user input. Examples of other ATs include screen magnifiers, cognitive support tools, speech command programs, and some brilliant new app that hasn’t been dreamed up yet. Further, assistive technologies of the same “type” may differ in how they present information, and users who share the same tool may further adjust settings to their liking. As web developers, we don’t necessarily need to make sure that each instance surfaces information identically, because each user’s preferences will not be exactly the same. Our aim is to ensure that no matter how a user chooses to explore our sites, content is perceivable, operable, understandable, and robust. By testing with a variety of assistive technologies—including but not limited to screen readers—we can help create a better web for all the many people who use it.

Further reading and resources

• WebAIM “Survey of Users with Low Vision”
• WebAIM “Screen Reader User Survey”
• W3C developer guides
  • W3C Web Accessibility Initiative (WAI) resources
  • Web Content Accessibility Guidelines (WCAG) 2.1
  • WAI-ARIA Authoring Practices 1.1
  • ARIA in HTML
  • Using ARIA
• W3C specifications: The docs below are known as “AAMs.” They detail how content maps into various accessibility APIs and may be less relevant to web developers’ day-to-day work. However, some have notes on how specific elements’ names and descriptions are meant to be calculated:
  • Core Accessibility API Mappings 1.1
  • Graphics Accessibility API Mappings
  • HTML Accessibility API Mappings 1.0
  • SVG Accessibility API Mappings
• Inclusive Components
• A List Apart articles on accessibility
  • “Conversational Semantics”
  • “WAI-finding with ARIA Landmark Roles”
• “The Importance of Manual Accessibility Testing”
• Deque University screen reader shortcuts references
• Screen reader user docs (commands)
  • JAWS user docs
  • Narrator user docs
  • NVDA user docs
  • VoiceOver user docs (VoiceOver command charts)
  • iOS VoiceOver user docs
• Browser rendering engine bug trackers
  • Chrome
  • Firefox
  • Microsoft Edge
  • Safari

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Hayden Library - PL1291.W793 2019

Hayden Library - P281.C765 2019

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Online Resource

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Liu, Zhuo, author

A collection of thoughts, experiences, ideas that I like, and ideas that I have been experimenting with over the last year. It covers HTML semantics, components and approaches to front-end architecture, class naming patterns, and HTTP compression.

About semantics

Semantics is the study of the relationships between signs and symbols and what they represent. In linguistics, this is primarily the study of the meaning of signs (such as words, phrases, or sounds) in language. In the context of front-end web development, semantics are largely concerned with the agreed meaning of HTML elements, attributes, and attribute values (including extensions like Microdata). These agreed semantics, which are usually formalised in specifications, can be used to help programmes (and subsequently humans) better understand aspects of the information on a website. However, even after formalisation, the semantics of elements, attributes, and attribute values are subject to adaptation and co-option by developers. This can lead to subsequent modifications of the formally agreed semantics (and is an HTML design principle).

Distinguishing between different types of HTML semantics

The principle of writing “semantic HTML” is one of the foundations of modern, professional front-end development. Most semantics are related to aspects of the nature of the existing or expected content (e.g. h1 element, lang attribute, email value of the type attribute, Microdata).

However, not all semantics need to be content-derived. Class names cannot be “unsemantic”. Whatever names are being used: they have meaning, they have purpose. Class name semantics can be different to those of HTML elements. We can leverage the agreed “global” semantics of HTML elements, certain HTML attributes, Microdata, etc., without confusing their purpose with those of the “local” website/application-specific semantics that are usually contained in the values of attributes like the class attribute.

Despite the HTML5 specification section on classes repeating the assumed “best practice” that…

…authors are encouraged to use [class attribute] values that describe the nature of the content, rather than values that describe the desired presentation of the content.

…there is no inherent reason to do this. In fact, it’s often a hindrance when working on large websites or applications.

• Content-layer semantics are already served by HTML elements and other attributes.
• Class names impart little or no useful semantic information to machines or human visitors unless it is part of a small set of agreed upon (and machine readable) names – Microformats.
• The primary purpose of a class name is to be a hook for CSS and JavaScript. If you don’t need to add presentation and behaviour to your web documents, then you probably don’t need classes in your HTML.
• Class names should communicate useful information to developers. It’s helpful to understand what a specific class name is going to do when you read a DOM snippet, especially in multi-developer teams where front-enders won’t be the only people working with HTML components.

Take this very simple example:

<div class="news">
    <h2>News</h2>
    [news content]
</div>

The class name news doesn’t tell you anything that is not already obvious from the content. It gives you no information about the architectural structure of the component, and it cannot be used with content that isn’t “news”. Tying your class name semantics tightly to the nature of the content has already reduced the ability of your architecture to scale or be easily put to use by other developers.

Content-independent class names

An alternative is to derive class name semantics from repeating structural and functional patterns in a design. The most reusable components are those with class names that are independent of the content.

We shouldn’t be afraid of making the connections between layers clear and explicit rather than having class names rigidly reflect specific content. Doing this doesn’t make classes “unsemantic”, it just means that their semantics are not derived from the content. We shouldn’t be afraid to include additional HTML elements if they help create more robust, flexible, and reusable components. Doing so does not make the HTML “unsemantic”, it just means that you use elements beyond the bare minimum needed to markup the content.

Front-end architecture

The aim of a component/template/object-oriented architecture is to be able to develop a limited number of reusable components that can contain a range of different content types. The important thing for class name semantics in non-trivial applications is that they be driven by pragmatism and best serve their primary purpose – providing meaningful, flexible, and reusable presentational/behavioural hooks for developers to use.

Reusable and combinable components

Scalable HTML/CSS must, by and large, rely on classes within the HTML to allow for the creation of reusable components. A flexible and reusable component is one which neither relies on existing within a certain part of the DOM tree, nor requires the use of specific element types. It should be able to adapt to different containers and be easily themed. If necessary, extra HTML elements (beyond those needed just to markup the content) and can be used to make the component more robust. A good example is what Nicole Sullivan calls the media object.

Components that can be easily combined benefit from the avoidance of type selectors in favour of classes. The following example prevents the easy combination of the btn component with the uilist component. The problems are that the specificity of .btn is less than that of .uilist a (which will override any shared properties), and the uilist component requires anchors as child nodes.

.btn { /* styles */ }
.uilist { /* styles */ }
.uilist a { /* styles */ }

<nav class="uilist">
    <a href="#">Home</a>
    <a href="#">About</a>
    <a class="btn" href="#">Login</a>
</nav>

An approach that improves the ease with which you can combine other components with uilist is to use classes to style the child DOM elements. Although this helps to reduce the specificity of the rule, the main benefit is that it gives you the option to apply the structural styles to any type of child node.

.btn { /* styles */ }
.uilist { /* styles */ }
.uilist-item { /* styles */ }

<nav class="uilist">
    <a class="uilist-item" href="#">Home</a>
    <a class="uilist-item" href="#">About</a>
    <span class="uilist-item">
        <a class="btn" href="#">Login</a>
    </span>
</nav>

JavaScript-specific classes

Using some form of JavaScript-specific classes can help to reduce the risk that thematic or structural changes to components will break any JavaScript that is also applied. An approach that I’ve found helpful is to use certain classes only for JavaScript hooks – js-* – and not to hang any presentation off them.

<a href="/login" class="btn btn-primary js-login"></a>

This way, you can reduce the chance that changing the structure or theme of components will inadvertently affect any required JavaScript behaviour and complex functionality.

Component modifiers

Components often have variants with slightly different presentations from the base component, e.g., a different coloured background or border. There are two mains patterns used to create these component variants. I’m going to call them the “single-class” and “multi-class” patterns.

The “single-class” pattern

.btn, .btn-primary { /* button template styles */ }
.btn-primary { /* styles specific to save button */ }

<button class="btn">Default</button>
<button class="btn-primary">Login</button>

The “multi-class” pattern

.btn { /* button template styles */ }
.btn-primary { /* styles specific to primary button */ }

<button class="btn">Default</button>
<button class="btn btn-primary">Login</button>

If you use a pre-processor, you might use Sass’s @extend functionality to reduce some of the maintenance work involved in using the “single-class” pattern. However, even with the help of a pre-processor, my preference is to use the “multi-class” pattern and add modifier classes in the HTML.

I’ve found it to be a more scalable pattern. For example, take the base btn component and add a further 5 types of button and 3 additional sizes. Using a “multi-class” pattern you end up with 9 classes that can be mixed-and-matched. Using a “single-class” pattern you end up with 24 classes.

It is also easier to make contextual tweaks to a component, if absolutely necessary. You might want to make small adjustments to any btn that appears within another component.

/* "multi-class" adjustment */
.thing .btn { /* adjustments */ }

/* "single-class" adjustment */
.thing .btn,
.thing .btn-primary,
.thing .btn-danger,
.thing .btn-etc { /* adjustments */ }

A “multi-class” pattern means you only need a single intra-component selector to target any type of btn-styled element within the component. A “single-class” pattern would mean that you may have to account for any possible button type, and adjust the selector whenever a new button variant is created.

Structured class names

When creating components – and “themes” that build upon them – some classes are used as component boundaries, some are used as component modifiers, and others are used to associate a collection of DOM nodes into a larger abstract presentational component.

It’s hard to deduce the relationship between btn (component), btn-primary (modifier), btn-group (component), and btn-group-item (component sub-object) because the names don’t clearly surface the purpose of the class. There is no consistent pattern.

In early 2011, I started experimenting with naming patterns that help me to more quickly understand the presentational relationship between nodes in a DOM snippet, rather than trying to piece together the site’s architecture by switching back-and-forth between HTML, CSS, and JS files. The notation in the gist is primarily influenced by the BEM system‘s approach to naming, but adapted into a form that I found easier to scan.

Since I first wrote this post, several other teams and frameworks have adopted this approach. MontageJS modified the notation into a different style, which I prefer and currently use in the SUIT framework:

/* Utility */
.u-utilityName {}

/* Component */
.ComponentName {}

/* Component modifier */
.ComponentName--modifierName {}

/* Component descendant */
.ComponentName-descendant {}

/* Component descendant modifier */
.ComponentName-descendant--modifierName {}

/* Component state (scoped to component) */
.ComponentName.is-stateOfComponent {}

This is merely a naming pattern that I’m finding helpful at the moment. It could take any form. But the benefit lies in removing the ambiguity of class names that rely only on (single) hyphens, or underscores, or camel case.

A note on raw file size and HTTP compression

Related to any discussion about modular/scalable CSS is a concern about file size and “bloat”. Nicole Sullivan’s talks often mention the file size savings (as well as maintenance improvements) that companies like Facebook experienced when adopting this kind of approach. Further to that, I thought I’d share my anecdotes about the effects of HTTP compression on pre-processor output and the extensive use of HTML classes.

When Twitter Bootstrap first came out, I rewrote the compiled CSS to better reflect how I would author it by hand and to compare the file sizes. After minifying both files, the hand-crafted CSS was about 10% smaller than the pre-processor output. But when both files were also gzipped, the pre-processor output was about 5% smaller than the hand-crafted CSS.

This highlights how important it is to compare the size of files after HTTP compression, because minified file sizes do not tell the whole story. It suggests that experienced CSS developers using pre-processors don’t need to be overly concerned about a certain degree of repetition in the compiled CSS because it can lend itself well to smaller file sizes after HTTP compression. The benefits of more maintainable “CSS” code via pre-processors should trump concerns about the aesthetics or size of the raw and minified output CSS.

In another experiment, I removed every class attribute from a 60KB HTML file pulled from a live site (already made up of many reusable components). Doing this reduced the file size to 25KB. When the original and stripped files were gzipped, their sizes were 7.6KB and 6KB respectively – a difference of 1.6KB. The actual file size consequences of liberal class use are rarely going to be worth stressing over.

How I learned to stop worrying…

The experience of many skilled developers, over many years, has led to a shift in how large-scale website and applications are developed. Despite this, for individuals weaned on an ideology where “semantic HTML” means using content-derived class names (and even then, only as a last resort), it usually requires you to work on a large application before you can become acutely aware of the impractical nature of that approach. You have to be prepared to disgard old ideas, look at alternatives, and even revisit ways that you may have previously dismissed.

Once you start writing non-trivial websites and applications that you and others must not only maintain but actively iterate upon, you quickly realise that despite your best efforts, your code starts to get harder and harder to maintain. It’s well worth taking the time to explore the work of some people who have proposed their own approaches to tackling these problems: Nicole’s blog and Object Oriented CSS project, Jonathan Snook’s Scalable Modular Architecture CSS, and the Block Element Modifier method that Yandex have developed.

When you choose to author HTML and CSS in a way that seeks to reduce the amount of time you spend writing and editing CSS, it involves accepting that you must instead spend more time changing HTML classes on elements if you want to change their styles. This turns out to be fairly practical, both for front-end and back-end developers – anyone can rearrange pre-built “lego blocks”; it turns out that no one can perform CSS-alchemy.