Componentware Revisited

I’m not a scholar, nor do I play one on TV, but when I search Google Scholar I find that I’m cited there a few times, most notably for a 1994 BYTE cover story, Componentware. The details there are at best of historical interest but the topic remains evergreen: How do we package software in ways that maximize its reusability while minimizing the level of skill required to achieve reuse?

By 1996 the web had booted up and I reprised the theme in On-Line Componentware1. That’s when it dawned on me that the websites that people “surfed” to were also software components that could be woven together to meet a variety of needs. It was my first glimpse of what we later came to know as SOA (service-oriented architecture), then RESTful APIs, and most recently microservices. Ever since then, wearing one hat or another, I’ve been elaborating the theme of that column: “A powerful capability for ad hoc distributed computing arises naturally from the architecture of the Web.” (link)

That architecture has in some ways remained the same, in other ways evolved dramatically, but its generative power continues to surprise and delight me. And I keep finding new ways to package and reuse web components.

Hypothesis has been a fascinating case study. Our web annotation system has two main components. The web service, written in Python, runs on a web server. The client, written in JavaScript, runs in your browser. Both are available for reuse in many different ways.

One way to reuse the web service is to embed views in web pages, as shown in this example from the Digital Polarization (Digipo) project:

The “Matching Annotations” widget embedded in that page is just this search result wrapped in an iframe. This is one of the most common and powerful ways to reuse web components.

The Hypothesis API affords another way to reuse its server component. The Timeline widget, embedded on that same page, works that way. It searches Hypothesis for the URLs of annotations tagged with the id of the current wiki page. Then it searches the annotations on each of those URLs for another user-assigned tag that signifies the publication date, and arranges those results chronologically. (The Timeline widget could have been written in PHP to run in the wiki server, but I’m more familiar with JavaScript so instead it’s written in JS and runs in the browser.)

The Hypothesis client can also be reused in powerful ways. Most notably, you can add the client to a website by including this simple script tag in the site’s main template:

Or you can use the Hypothesis proxy,, to inject the client into a web page, for example:

When you use Hypothesis to annotate a PDF file, it relies on a separate component — Mozilla’s PDF.js — to parse the PDF and render it in the browser so the Hypothesis client can operate on it. PDF.js is available natively in Firefox, the Hypothesis Chrome extension injects it when you annotate a PDF in that browser.

Another Hypothesis component, pdf.js-hypothesis, enables a web server to serve a PDF with PDF.js and Hypothesis both active. That makes PDF annotation available in any browser. We use it in our prototype Canvas app, for example, to serve annotation-enabled PDFs in the Canvas learming management system (LMS).

Still another component enables custom rendering of annotations. You can see it in action at Science in the Classroom, a collection of research papers annotated to serve as teaching materials.

Graduate students use Hypothesis to create the annotations. But Science in the Classroom prefers to display them using its own mechanism, Learning Lens. So when the page loads, it fetches annotations using the Hypothesis API and then paints them on the page using a component that’s part of the Hypothesis client but is also available as the standalone NPM module dom-anchor-text-quote.

I am deliberately blurring the definition of web component because I think it properly encompasses many different things: a web page embedded in an iframe; an API-accessible web service; a rich client application like Hypothesis (or a simple widget like the Timeline) embedded in a web page; a standalone module like dom-anchor-text-quote; a repackaging of Hypothesis as a WordPress plugin or a Canvanas external tool.

This is a rich assortment of ingredients! But there’s one that’s notably absent. We’ve seen lots of ways to use the Hypothesis client as a component that plugs into other environments and makes annotation available there. But what if you want to plug something into the Hypothesis client? There isn’t yet a mechanism for that. The code is open source and can be modified, as Marija Katic and Martin Eve have done with Annotran, a translation tool based on Hypothesis. That’s a great example of code reuse. But it isn’t, at least to my way of thinking, an example of component reuse. Although I recognize many different species of software components, they all share one piece of common DNA: reuse without internal modification.

In an essay on what I learned while building the Canvas app, I noted two critical aspects of the healthy ecosystem that Canvas and other learning management systems inhabit:

1. Standard protocols. In the LMS world, Learning Tools Interoperability (LTI) defines those protocols.

2. Frictionless component reuse. This flows from item 1. An LTI app expects to be launched from an LMS and to run embedded in an iframe there. Again, this is the most common and powerful way to reuse web components.

The question I asked there, and tried to answer: Could an iframe embed web components within a rich web client like Hypothesis? If so that might open the way for features not yet in the Hypothesis core, like controlled tagging, that would otherwise require deep surgery on the Hypothesis client, and intimate knowledge of its JavaScript framework (Angular) and the nonstandard component model dictated by that framework.

I had already tried a couple of experiments to add controlled tagging to the Hypothesis client. In this one, the tag suggestions offered in the tag editor are bound to Hypothesis groups. In this one, tag suggestions are bound to an external web service. Both experiments entailed nontrivial alteration of the Hypothesis client.

In a third experiment, I modified the Hypothesis client in a way that could enable a family of components to plug into it. This customized client embedded an iframe in the annotation editor, and launched a user-defined web application into that iframe, passing it one parameter: the id of the annotation open in the editor. Because it was configured with the credentials of a Hypothesis user, it could work as a pluggable component that communicates with the active annotation and also with the full panoply of web resources. You could, perhaps, think of it as an annotation applet. Here’s a demo.

This approach was intriguing and might serve some useful purposes, but an iframe is an ugly and awkward construct to stick into the middle of a richly-designed web client. And this approach again fails my definition of component reuse because it requires internal modification of the client.

So as I began working to integrate Hypothesis into Digipo I was still looking for a way to control Hypothesis tags without modifying the Hypothesis client. As described in A toolkit for fact checkers, we initially used bookmarklets to do that, then began developing a Chrome extension for the Digipo project.

The Chrome extension immediately solved a couple of vexing problems. It enabled us to cleanly package a growing set of Digipo tools, by making them conveniently right-click-accessible. And it got around the security constraints that increasingly make bookmarklets untenable.

Just as importantly it enabled us to blend together a Digipo-specific set of tools, some but not all of which are Hypothesis-powered. For a Digipo fact checker, Hypothesis isn’t a primary part of the experience. It’s a supporting component that’s brought into the process as and where needed. It’s infrastructure.

The Digipo workflow relies on controlled tagging to accumulate evidence into several buckets associated with each investigation. When you’re on a page that you want to put into a bucket, you can use Digipo’s Tag this Page helper to create a Hypothesis page note with the tag for that investigation. It starts here:

That leads to a page that lists the Digipo investigations.

When you choose one, the extension uses the Hypothesis API to create a page note with the investigation’s tag.

Thanks to Hypothesis direct linking, the interaction flows seamlessly from the Digipo extension to Hypothesis. You land in the annotation editor where you can do more with Hypothesis: add comments and new tags, discuss the target document with other Hypothesis users.

But this arrangement only creates Hypothesis page notes: annotations that refer to a target document but not to a selection within that document. More powerful uses of Hypothesis flow from selections within target documents. Could a selection-based annotation begin in the Digipo extension, acquire a tag, and then flow through to Hypothesis?

Happily the answer is yes. You can see that here.

The Digipo Chrome extension presents one set of helpers when you right-click on a page with nothing selected. Some of the helpers rely on Hypothesis, others just automate parts of the Digipo workflow — for example, launching advanced Google searches. When you right-click with a selection active, the Digipo Chrome extension presents another set of helpers which, again, may or may not rely on Hypothesis. One of them, Tag this Selection, works like Tag this Page in that it uses the Hypothesis API to create an annotation that includes a controlled tag. But Tag this Selection does a bit more work. It sends not only the URL of the target document, but also a Text Quote Selector that anchors the annotation within the document. In this case, too, the interaction then flows seamlessly into Hypothesis where you can edit the newly-created annotation and perhaps discuss the selected passage.

You can see more of the interplay between the Digipo and Hypothesis extensions in this screencast. I’m pretty excited by how this is turning out. The Digipo extension is Chrome-only for now, as is the Hypothesis extension, but WebExtensions should soon enable broader coverage. There’s still a need to plug packaged behavior directly into the Hypothesis client. But much can be accomplished with an extension that cooperates with Hypothesis using its existing set of affordances. The Digipo extension is one example. I can imagine many others, and I’m expanding my definition of componentware to include them.

1 I love how our copy editor insisted on hyphenating On-Line!

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