Controlled Vocabularies and Tags in a Catalogue

If you ask ten people to describe the same product in three words, you will get thirty words and perhaps twenty different ideas. One says "planner", another "scheduler", a third "calendar tool". All are right. For a person browsing, the variety is harmless. For a catalogue that must let someone find every scheduling tool, the variety is a problem. Which word do they look under?

The library's answer, developed over generations, is the controlled vocabulary. The web's answer, in many places, is tags. Most good catalogues use something of both. This guide explains the two approaches, their strengths and weaknesses, and how to describe a product in words a catalogue can use.

Two ways to label

A controlled vocabulary

A controlled vocabulary is a carefully selected list of words and phrases used to tag items so that they can be retrieved more easily. The key word is controlled: editors decide which terms are allowed and what each means. A thing is described using the approved term, even if the creator used another word.

Features of a good controlled vocabulary:

• One preferred term per concept. "Scheduling" is chosen, and "planner", "calendar tool" and "appointments" are recorded as variants that lead to it.
• Defined meaning, so editors apply it consistently.
• Relationships between terms. Broader terms, narrower terms and related terms.
• Rules for adding and changing terms.

A thesaurus, in the information retrieval sense, is a controlled vocabulary with these relationships shown. "Productivity" might be broader than "Scheduling", which might be broader than "Appointment booking".

Tags and folksonomies

Tags are labels that users or makers attach freely. A system where users create and apply their own tags, producing a loosely organised collection of labels, is called a folksonomy.

Features:

• Flexible. Anyone can add a term.
• Current. New terms appear as soon as people use them.
• Messy. Spelling variants, synonyms, plurals, abbreviations and personal quirks multiply.
• Uneven. Some items are richly tagged and others not at all.

What each does well

A controlled vocabulary gives:

• Precision. A search for a term returns items about that concept.
• Recall. Variants are mapped to the preferred term, so synonyms still find the item.
• Consistency. Similar items are described alike.
• Browsing structure. Hierarchies let readers move from general to specific.

Tags give:

• Speed. No committee is needed to add a term.
• Discovery. You see what people actually call things.
• Coverage of the new. Emerging ideas appear first as tags.
• Personal fit. Makers can describe what matters to them.

What each does badly

A controlled vocabulary:

• Takes effort to build and maintain.
• Can lag behind new ideas.
• May not match everyday language.
• Can feel rigid.

Tags:

• Fragment: "e-commerce", "ecommerce" and "online shop" scatter items.
• Include noise, such as vague or promotional terms.
• Have no hierarchy.
• Can be abused, with irrelevant popular tags added to attract attention.

Mixing the two

Many catalogues use a hybrid.

• A controlled list of categories for the main subject, applied by editors or chosen by makers from a fixed menu.
• Free tags for features and flavour, added by makers, with editors merging duplicates.
• A review process that watches popular tags and promotes them into the controlled vocabulary when they prove useful.

This keeps the benefits of both. The controlled list provides structure; the tags provide life.

How to choose terms for your product

If you are describing a product in a catalogue, a few habits help.

Start with the user's words

How would someone who needs your product describe what they want? Use their words, not your internal ones. Look at how similar products are described.

Choose the preferred term from the menu

If the catalogue offers a fixed list, pick the closest. Do not stretch a term to cover something it does not mean, and do not pick a popular category merely because it is crowded with visitors.

Use specific terms over general ones

"Appointment booking for clinics" is more useful than "business". Where the vocabulary has levels, choose the most specific that fits.

Add a few tags, not many

Three to six tags that describe main aspects are better than twenty. Each should be something you would defend as true.

• What it does: the task.
• For whom: the audience.
• Where it runs: the platform.
• How it works: a key feature.

Avoid weak tags

• Hype: "best", "powerful", "awesome".
• Generic words: "app", "tool", "software".
• Irrelevant popular terms. This is tag spam.
• Brand names you do not own.

Use consistent forms

Choose singular or plural as the catalogue prefers. Choose a spelling and keep it. Avoid abbreviations unless they are standard.

Describe in plain words as well

Tags and terms do not replace a description. Write a clear sentence or two beside them, because some readers will never use the tags.

For editors: building a vocabulary

If you run a catalogue, a few principles help.

Start small and grow. A short, clear list of top-level categories is better than a long, confusing one.

Write definitions. One sentence for each term, with examples of what belongs and what does not.

Record variants. For each preferred term, list the other words people use. Make them lead to the preferred term.

Show relationships. Broader, narrower and related.

Watch the tags. Review the most-used free tags regularly. Merge duplicates, correct spellings and promote strong ones.

Retire gently. When a term is replaced, redirect it. Do not strand old records.

Publish the list. Makers and readers should be able to see the vocabulary.

Review with users. Ask people what they could not find.

Avoid over-engineering. A vocabulary nobody can maintain becomes stale.

Subject indexing in brief

The practice of describing a document's content with terms from a vocabulary is called subject indexing. It has two sides. The indexer must decide what the item is about and choose terms that capture it, and the user must be able to guess or discover those terms. A good catalogue helps both: it guides indexers with definitions and guides users with suggestions and "see" references.

When a reader types a non-preferred term, the catalogue should say: "Planner: see Scheduling." That tiny courtesy turns a dead end into a door.

Accessibility and clarity

Terms and tags are text, and they should be readable to everyone.

• Use plain words.
• Avoid symbols and emoji as tags.
• Make tag lists navigable by keyboard.
• Do not rely on colour to distinguish categories.
• Provide text equivalents for icons.

A short worked example

A maker lists a tool that lets small clinics take bookings online. The catalogue offers a controlled list with "Scheduling" under "Productivity", and free tags. She picks "Scheduling" as the category and adds the tags "clinics", "online booking", "reminders" and "browser". An editor sees that another entry uses "appointment booking", links it to the same preferred term and adds "appointment booking" as a variant, so that a search for either finds both. A reader who types "planner" sees "Planner: see Scheduling" and arrives in the right place.

Nothing about the process was grand. It was a series of small agreements about words, and it made the catalogue findable.

Common mistakes

• Too many tags.
• Hype and generic tags.
• Misusing categories.
• Inconsistent spellings.
• No variants recorded.
• A vocabulary no one maintains.
• Tag spam.
• No plain description.

On this site

The categories page shows the controlled list of subjects used here, the search page finds entries by words, including variants, and the launches page shows entries with their categories. The submit page is where you choose a category and describe your product, and the contact page reaches a person if you cannot find a fitting term.

Three small cases

A synonym trap. A maker tags a tool "planner". The catalogue's preferred term is "Scheduling". A reader browsing Scheduling never sees it. The fix is a variant record: "planner" leads to "Scheduling", and the entry is filed under the preferred term. Nothing about the product changed; the vocabulary simply caught up with the language people use.

A tag explosion. Over a year, makers add "ecommerce", "e-commerce", "online store", "web shop" and "webshop". An editor reviews the most-used tags, chooses "E-commerce" as the preferred term, maps the rest to it and merges the entries. Search results become one list instead of five.

A new idea. A new kind of product appears for which no category exists. Makers tag it in a dozen ways. Editors watch the pattern, agree a definition and add a new term with variants. The vocabulary grows because the tags showed the need. This is the healthy cycle: free labels discover, a controlled list consolidates.

Maintaining the list

A vocabulary is a garden. Prune what is unused, split what has grown too broad and merge what overlaps. Record each change with a date and a reason so that old records can be understood. Tell makers when terms change, and keep old terms as variants so that nothing becomes unreachable. The goal is not a perfect list but a living, understood one.

The short version

A controlled vocabulary fixes one preferred term per concept and maps variants to it; tags are free and flexible and messy. Good catalogues use both: a controlled list for the main subject, curated tags for flavour and a habit of promoting useful tags. When describing your product, use the user's words, pick the most specific preferred term, add a few honest tags, avoid hype and write a plain description beside them. Words are how a catalogue finds things.