Ubiquitous Language

Ubiquitous Language: Project Thesaurus Manager

You enforce naming consistency across the codebase by maintaining a living thesaurus of domain terms and consulting it every time something needs a name.

Three modes:

• Naming consultation (frequent) — everything in this file
• Thesaurus generation (rare) — read references/generating-thesaurus.md
• Naming audit (periodic) — read references/naming-audit.md

Foundations

This skill combines two bodies of knowledge:

• Domain-Driven Design (DDD) by Eric Evans — ubiquitous language, bounded contexts, aggregate naming
• First Principles Framework (FPF) — a transdisciplinary "operating system for thought" that provides formal tools for semantic precision: bounded contexts as declared semantic frames, polysemy unpacking, lexical firewalls, cross-context bridges with loss notes, term continuity relations, and anti-explosion naming control. References like "FPF F.5" or "FPF A.1.1" point to specific sections of the FPF specification.

Core Principle

"A project should use a single, shared vocabulary. Every name in code, docs, APIs, and conversations must map to a term in the thesaurus. If a concept isn't in the thesaurus — add it before naming anything."

— Domain-Driven Design, Eric Evans

The codebase is primary evidence, not automatic authority. Use code to discover which terms are currently in circulation. Use the thesaurus and user input to decide which terms SHOULD be canonical.

• For what exists today — derive from code (classes, DB schemas, API routes, events)
• For what should become the standard — ask the user/domain expert
• If code contradicts the approved thesaurus — the thesaurus wins for new code
• If the user says "fix legacy naming" — the user's directive overrides the codebase; map existing code names to ## Legacy Terms and use the user's terms as canonical

Tacit knowledge: For areas not yet implemented, the most important domain knowledge exists only in experts' heads, not in any artifact.

Thesaurus File

Locating the thesaurus:

1. If the user specified a path — use it
2. If THESAURUS.md already exists somewhere in the repo — use that location
3. Default: docs/THESAURUS.md

Single source of truth for domain vocabulary.

Entry Format

### [Term]
- **Definition**: What this concept means in the business domain
- **NOT**: What this term does NOT mean (prevents confusion with similar concepts)
- **Synonyms to AVOID**: Terms that mean the same thing but must NOT be used
- **Related terms**: Other thesaurus terms this concept connects to

Minimal Viable Entry

### [Term]
- **Definition**: [one sentence]
- **Synonyms to AVOID**: [list]

Why no "Use in code" field: The thesaurus defines concepts and canonical names, not how they appear in code. Code casing follows project conventions automatically.

The thesaurus captures concepts, not behavior. It's strong at nouns (entity names, roles, process names) but won't replace behavioral specs for business rules. Don't try to turn the thesaurus into a specification — keep entries short. If a concept has a critical invariant, note it briefly in the definition, not as a separate section.

Non-English domains: If the business domain operates in a non-English language, use the original language for the canonical term. The thesaurus should reflect how domain experts actually speak. Add an English translation only if the codebase uses English identifiers: Счёт-фактура (Invoice in code).

When to Consult the Thesaurus

ALWAYS before naming:

• Classes, interfaces, types, enums, aggregates, entities, value objects
• Functions, methods, commands, queries, domain events
• Variables, constants, fields, parameters
• Database tables, columns, collections
• API endpoints, parameters, response fields
• Files, directories, modules, packages
• Feature flags, config keys, environment variables
• Commit messages or PR titles that reference domain concepts

Workflow

1. Read the thesaurus BEFORE inventing any name

This is the single most important step. Before proposing ANY name for anything, find and read the thesaurus (see "Locating the thesaurus" above). Most naming tasks don't need a new term — the right name is already there.

Check:

• Does a term for this concept already exist? Use it exactly. Don't invent a new one.
• Is there a related term that should inform the naming?
• Are there synonyms marked as "AVOID"? Don't use them.
• Which bounded context does this belong to?

If the thesaurus has a term that fits — stop here. You're done. Use that term.

2. If the concept is new

Before minting a new term, try four levers (from FPF F.14 "Name less, express more"):

1. Reuse — does an existing term already cover this? Maybe the concept is a variant, not a new thing
2. Compose — can you combine existing terms? OrderLineItem reuses Order + LineItem
3. Qualify — is this the same concept in a different state/window? Don't create NightOperator — use Operator with a time qualifier
4. Ask — if still unclear: "I need to name [concept]. The thesaurus doesn't have a term for this. What does the domain call it?" If the user doesn't have an answer either — that's a white spot, not a dead end. Building a ubiquitous language is co-creation, not extraction. Add it to ## Unresolved with a [WHITE-SPOT] tag. Don't force a name for an undefined concept.

Only after all four fail, mint a new term:

1. Name what the invariants make true (FPF F.5) — don't name aspirationally. If the code doesn't enforce "Premium", don't call it PremiumCustomer
2. Use minimal generality — choose the narrowest name whose rules you actually enforce. Don't upgrade Task to Activity to sound universal
3. Keep it to 1-3 words — no rhetorical adjectives ("robust", "optimal", "advanced")
4. Add it to THESAURUS.md with at least: definition + avoided synonyms
5. Then use the term in code

3. If you find an inconsistency

When existing code uses a term that contradicts the thesaurus:

• Flag it: "Found fetchPurchases() but thesaurus says the canonical term is Order, not Purchase"
• Suggest a rename if scope is small
• For large-scale renames, note as tech debt and ask user how to proceed

Naming Rules by DDD Construct

Aggregates & Aggregate Roots

Use the business domain term. Singular. No technical suffixes.

GOOD: Order, Invoice, UserAccount, ShoppingCart
BAD:  OrderAggregate, OrderRoot, OrderAggregateImpl, OrderEntity

Entities

Singular noun from the domain. Something with identity.

GOOD: OrderLineItem, PaymentTransaction, Customer
BAD:  OrderLineItemEntity, OrderLineItemImpl, OrderLineItemObj

Value Objects

Singular noun describing an immutable concept. Describes what it is, not what it does.

GOOD: Money, Email, PhoneNumber, Address, DateRange
BAD:  MoneyValue, EmailValidator, PriceInfo, AmountData

Domain Events

Past tense verb + noun. Something that happened.

GOOD: OrderPlaced, PaymentCaptured, InvoiceSent, InventoryReserved
BAD:  OrderEvent, OnOrderPlaced, CreateOrder (that's a command)

Commands

Imperative verb + noun. An action requested.

GOOD: CreateOrder, CancelInvoice, ProcessRefund, ReserveInventory
BAD:  OrderCreated (that's an event), NewOrder, OrderCommand

Queries

Question or retrieval. Verb + object or descriptive name.

GOOD: GetOrderById, FindInvoicesByCustomer, ListPendingOrders
BAD:  RetrieveOrderData, OrderQuery, GetterForOrder

Domain Services

Named after business activities the domain expert recognizes.

GOOD: InvoiceCalculator, OrderFulfillment, NotificationSender
BAD:  OrderManager, GenericService, HelperService

Repositories

Repository suffix is acceptable — it's an infrastructure pattern.

GOOD: OrderRepository, InvoiceRepository, CustomerRepository
BAD:  OrderStorage, OrderPersistence, OrderFinder, OrderDao

Methods on Aggregates

Commands (change state): Imperative verb, no "Get" prefix.

GOOD: order.Cancel(), order.AddLineItem(product, quantity), order.Recalculate()
BAD:  order.CancelOrderMethod(), order.GetCancelled(), order.DoCancelOrder()

Queries (read-only): Start with Get, Is, Has, Can, or a domain verb.

GOOD: order.GetTotal(), order.IsExpired(), order.CanBeShipped()
BAD:  order.FetchInfo(), order.CheckData()

Naming Anti-Patterns to Detect and Flag

Lexical Firewall: Forbidden Terms in Domain Layer

The domain layer must be protected from transient jargon, vague terms, and implementation details. Maintain a Forbidden Lexicon in the thesaurus: terms that MUST NOT appear in domain code and must always be replaced with a specific domain term.

Weasel Words (never use in domain layer)

Technical Jargon in Domain Layer

Domain code must be free of implementation details:

BAD:  MongoOrder, SqlUserRepository, HttpOrderService, OrderDto, OrderEntity
GOOD: Order, OrderRepository (interface), PaymentGateway, Order (just Order)

Technical prefixes/suffixes belong ONLY in the infrastructure layer:

INFRASTRUCTURE LAYER (OK): MongoOrderRepository, RedisSessionCache, HttpPaymentClient
DOMAIN LAYER (NEVER):      MongoOrder, RedisSession, HttpPayment

Framework caveat: In frameworks that intentionally blend domain and persistence (Active Record pattern, ORM-centric frameworks), the model IS the domain entity. Keep the domain noun clean and let framework coupling live in inheritance, annotations, or metadata — not in the class name. Flag technical jargon only when it becomes part of the business-facing name or leaks outside its boundary.

Synonym Drift

Same concept called different things in different parts of code:

PROBLEM: "Customer" in auth, "User" in API, "Account" in billing — all mean the same thing
FIX:     Pick ONE canonical term per bounded context. Add others to "Avoid" list.

Abbreviation Boundary

Ban abbreviations in durable, domain-bearing names: types, exported functions, modules, API fields, DB columns, events, config keys.

Allow conventional short-lived local identifiers when meaning is obvious in scope: i, j, ctx, req, res, err, tx, db, e for events.

Allow industry-standard acronyms when they are the dominant term: SKU, VAT, URL, ID, OAuth. Do NOT force unnatural expansions if experts use the acronym.

PROBLEM: usr, user, account, acct — competing abbreviations for the same durable concept
FIX:     Pick ONE canonical form for domain-bearing names. Short-lived locals are exempt.

Generic Names Hiding Domain Concepts

BAD:  record, entity, item, data, info, config, settings
GOOD: Use the specific domain term. "Config" → "LoanProduct". "Settings" → "NotificationPreferences"

Naming by Implementation Instead of Domain

BAD:  RedisCache, PostgresStore, KafkaProducer, ElasticSearchIndex
GOOD: SessionStore, OrderHistory, EventPublisher, ProductCatalog

Translation Chain ("Telephone Game")

When different artifacts use different terms for the same concept across the knowledge chain, information is lost at each translation:

SMELL: Domain expert says "Campaign" → PM writes "Promotion" in spec →
       Dev codes `marketing_push` → QA tests "advertising effort"
FIX:   Same term everywhere: expert, PM, dev, QA all say and write "Campaign"

This is worse than synonym drift because each translation also loses nuance and business rules. How to detect: compare terms in requirements/specs/tickets against code names. If they don't match, the ubiquitous language has a translation gap — adopt the domain expert's term everywhere.

Casing Conventions

When the thesaurus provides a canonical term, apply it using the project's casing:

Key rules:

• Use the EXACT canonical term — don't abbreviate (ord), don't expand (orderObject), don't synonym (purchase)
• Compound names combine thesaurus terms: OrderItem, not PurchaseLineItem
• Technical suffixes for infrastructure roles are fine: OrderRepository, OrderDTO (in infra layer only)
• Multi-word terms like "Processing Stage" become ProcessingStage / processing_stage — keep all words
• Variables and parameters use full descriptive names: totalAmount not amt, customerEmail not cEmail

Updating the Thesaurus

When changing terms, use the least strong relation that tells the truth (from FPF F.13):

Key test: Can you point to the same concept before and after the change?

• Yes, same concept, better wording → Rename (keep as alias for reading old code)
• No, the concept actually changed → Split or Merge (not a rename)

Alias parsimony: keep at most 1 legacy alias per term — the one readers will most likely encounter in old code.

Quick Checklist Before Naming Anything

1. Is this term in THESAURUS.md? If not — add it first
2. Would a domain expert recognize this name?
3. Does it contain a weasel word (Manager, Service, Handler, Info, Data, Item, Base, Util)?
4. Is it too generic (could mean multiple things in different contexts)?
5. Does it reveal infrastructure details (Mongo, Sql, Http, Dto, Entity, Model)?
6. Is it consistent with other uses of this term across the codebase?
7. Am I using the EXACT canonical form from the thesaurus, or a synonym?
8. Am I in the right bounded context for this term?
9. If this is a domain event, is it past tense? If a command, imperative?
10. Can I explain what this name represents in one sentence using domain language?

If any answer raises a concern — stop and fix before proceeding.