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Web App Product Ontologies

Web apps with user interfaces lend themselves to object-orientation. It’s in the middle of the acronym: Document Object Model. This isn’t to say you a “functional” product model is impossible, but visualizing a function involves expressing it with an object; to shoehorn a product model into a UI is to congeal it into an assemblage of objects.

Articulating a good product model requires picking the most expressive classes of objects and describing how they’re conceptually related: developing a product ontology.1

Formal XML-derived syntaxes have been developed for physical product ontology, but the primacy of physical components makes them awkward fits for describing the product models behind web applications. Whereas physical product ontologies describe concrete units—an air purifier with one fan assembly and one filter assembly, working together—a web product model is essentially nonconcrete until runtime.

Lee and Suh’s meta-product ontology divides entities into physical and abstract entities.2 Web app product models rarely have equivalents to physical Objects (global and static), but deal heavily in SetOrClass and Datatype entities that are instantiated by users.

Rather than describing a collection of identifiable entities and their relations, then, a description of a web product specifies classes of entities and the relations between their classes. A user who udnerstands those classes and relations can use the product to express and control the concrete, identifiable stuff.

In some respects, this is an easier task than developing a formal language for describing air purifiers! Web product planning can borrow the notion of an underlying, describable ontology without falling into the mire of rigidity/nonrigidity, subassemblies, and so on. Because the product’s implementation in code is an unambiguous and analyzable expression of the product’s structure, a web product-modeler doesn’t have to be as exhaustive.

What are your product’s primary concepts, its objects under manipulation? When a user uses your product, what do they control?

I think of this as nailing down a product model’s noumena, those stubborn concepts that persist independent of their representation. Whether or not they’re expressed directly—whether or not the user even conceives of the product in their terms—these are the product’s underlying objects. An app for scheduling events, no matter what interface exposes, works with some internal notion of what constitutes an “event;” this is its primary noumenal class.3

Describing noumena and interdependencies early could kick off data model design before, or concurrently with, interface design. A well-expressed product model can be the joint precursor to both, rather than building one to fit the other.

That said, sketching a product ontology shouldn’t be mistaken for data model design. The engineering task is to produce a data model that can unambiguously represent the space of permitted product model states. There may be multiple data models that achieve this. In my experience, a single product model will be implemented and reimplemented with a succession of data models before it’s changed.

As a result, it’s easy to think through other products’ ontologies without thinking about the details of their implementation.

An pleasant example: Trello is essentially a tool for organizing cards representing records. Their product involves other nouns—lists, boards, etc.—these are derivative concepts for organizing and displaying cards. Regardless of whether you click on a card on a board, in a calendar view, or in the archived query view (when a card has been disassociated from its board/list), the card is readable and editable in exactly the same popover format. Easy to recall, easy to teach.

An unpleasant example: I can’t think up a tight product ontology for Notion. Is it for organizing records (in table or gallery views)? Is it for organizing lightly interactive pages, like a wiki with embedded forms? Or am I organizing the sections of content on those pages, which are drag-and-drop rearrangebale? There must be some underlying consistent data model, but I can’t find it in the fog of concepts and interactions.

A good product teaches its users to perceive its abstract product model, and to intuit based on their understanding thereof. While the noumena in that model may not be represented directly or consistently, users will learn them more effectively when they are.

Controlling noumena

We can turn sketched classes of product entities into a fistful of representational litmus tests. The product we build around our ontology will necessarily involve mechanisms for users to view, organize, and modify our noumena. Representing the entities in the product model directly and comprehensively should keep the user’s model of the system state close to the system’s internal state; keeping a user’s understanding accurate should minimize corrective error.4

Consider your product as a control interface for each class of entities: how ergonomically can a user assess the state of an entity and cause precisely the represented change they intend? To that end…

The Cognitive Dimensions of Notations framework6 is a list of digital product usability anti-patterns (with some neat properties, e.g. pairwise independence. It may seem a stretch to think of web apps as “notations,” but these antipatterns can appear anywhere users do composition (whether they’re composing a vacation, their account settings, or a program). Users work to get a product to express their intent. Blandford and Green turned the Cognitive Dimensions of Notation into a set of usability litmus tests like the ones I propose above.7

Besides this usability-forecasting, a well-specified product model offers a nice starting point for breaking a product into reusable components. It might be sensible to build a single component to manage representing a noumenon in a variety of contexts; “cards” (neatly arranged into arrays; vertically more forgiving than table rows) are a common pattern for this. If certain contexts require the card to be too compact to be a good control surface, clicking on it can pop a more articulate modal:8 picking noumena that exist independent of outside context should mitigate the context-downside of hiding the rest of the page.

Comparative advantage

Instead of beginning with ontology, we could begin with functionalism: “what do users want to do with our product?” This doesn’t avoid creating a product ontology, but it defers to an imaginary user’s incumbent ontology. If a product would simplify a complex workflow, this approach cements into its heart an model just as unwieldy as the one it should replace.9

Focusing on user workflows too early also runs the risk of tailoring our data model too closely to a particular representation that achieves a very specific function. Since representations are immediately user-facing, they’re more likely than the data models to be subject to early user feedback and iteration. Better to build a flexible data model and leave our UI easy to invalidate.

Directness and comprehensiveness are useful heuristics for UI options. Conversational interfaces are hip for their humanism, but a conversation with intense control requirements is frustrating: it’s untransparent, which makes it error prone.


  1. This goal is complicated by the reflexive relationship between a product’s ontology and its functionality. Some ontology might achieve a product’s functional intent better than others… but the functions users desire are themselves formed through their understanding of the product model, and they can more articulately communicate desires in terms of the product concepts that are named for them. An ontology-axiology bind!↩︎

  2. Lee, Jae-Hyun, and Hyo-Won Suh. “OWL-based product ontology architecture and representation for sharing product knowledge on a web.” In International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, vol. 48035, pp. 853-861. 2007.↩︎

  3. I’m self-conscious about “noumenon” being a pretentious term, but there’s a utility for me in setting up an unfamiliar category. Terms like “entity” or “object” are overloaded (esp. “object,” in an essay that’s essentially about preferring object-oriented representations for noumena).

    It should be clear that we’re not talking about the instance a user perceives and interacts with. A user’s perception of the product model is wont to be inaccurate; whether there’s really a correct perception of a product model feels like a question for metaphysics.

    A user’s perception of the product model may be more or less close to the designed product model, though, and the control systems reading I reference supports my opinion that closeness here is good. The term “noumenon” emphasizes the fallability of the UI phenomena you build.↩︎

  4. I’ve been poking thorugh Åström, Karl Johan, and Richard M. Murray. Feedback systems: an introduction for scientists and engineers. Princeton university press, 2010.↩︎

  5. “Position control” and “direct control” are terms taken from Abrecht, Blake, and N. G. Leveson. “Systems theoretic process analysis (STPA) of an offshore supply vessel dynamic positioning system.” Massachusetts Institute of Technology, Cambridge, MA (2016).↩︎

  6. The Cognitive Dimensions are decently summarized on Wikipedia, but more clearly in Blackwell, Alan, and Thomas Green. “Notational systems - the cognitive dimensions of notations framework.” HCI models, theories, and frameworks: toward an interdisciplinary science. Morgan Kaufmann (2003).↩︎

  7. Blandford, Ann, and Thomas Green. “OSM: an ontology-based approach to usability evaluation.” Note: the notion of user-private, device-private, and shared concepts butts up againts my idea of a “noumenon” here, but more value-neutrally. In my mind, the noumena form a starting set of shared concepts.↩︎

  8. Trello does this, but Airtable’s modal view for a record is a great example from a more complex product. Sometimes the record is a row in a table; sometimes it’s a card in a gallery; no matter what, clicking on it will reveal all the data for the record and allow you to directly modify any of it. No matter the representation, the user is one modal-expanding click away from a consistent control experience.↩︎

  9. Additionally, users are nonhomogeneous; overfitting to your early users’ mental models might be a mistake. This is especially true for teams with the ambition to shift up/down-market or stretch their product into new applications, or strong selection biases in their initial user base (e.g. a bias towards users from a certain accelerator cohort).↩︎