The ubiquitous language must be precise and consistent. It should eliminate the need for assumptions and should make the business domain’s logic explicit.

Since ambiguity hinders communication, each term of the ubiquitous language should have one and only one meaning. Let’s look at a few examples of unclear termi‐ nology and how it can be improved.

Ambiguous terms

Let’s say that in some business domain, the term policy has multiple meanings: it can mean a regulatory rule or an insurance contract. The exact meaning can be worked out in human-to-human interaction, depending on the context. Software, however, doesn’t cope well with ambiguity, and it can be cumbersome and challenging to model the “policy” entity in code.

Ubiquitous language demands a single meaning for each term, so “policy” should be modeled explicitly using the two terms regulatory rule and insurance contract.

Synonymous terms

Two terms cannot be used interchangeably in a ubiquitous language. For example, many systems use the term user. However, a careful examination of the domain experts’ lingo may reveal that user and other terms are used interchangeably: for example, user, visitor, administrator, account, etc.

Synonymous terms can seem harmless at first. However, in most cases, they denote different concepts. In this example, both visitor and account technically refer to the system’s users; however, in most systems, unregistered and registered users represent different roles and have different behaviors. For example, the “visitors” data is used mainly for analysis purposes, whereas “accounts” actually uses the system and its functionality.

It is preferable to use each term explicitly in its specific context. Understanding the differences between the terms in use allows for building simpler and clearer models and implementations of the business domain’s entities.