Class diagram reading instructions
Class diagrams consist of ‘entities’, the relationships between the entities, and the data contained within the entities. An entity represents a certain physical or logical (data) entity. Examples of entities include accounting point and sales agreement. Examples of entities occurring in messaging are shown in the picture below.
The names of the entities are written in bold at the top of the box describing the entity.
The entity’s attributes, or data fields, are listed below the line underneath the name. The square brackets following the attributes define the attribute's multiplicity, or information as to how many values a data field can or will contain. For example, [0..1] means that the field is optional (or only compulsory in certain situations) and [1] means that the value is compulsory. If there may be an unspecified number of values, the * sign is used. The same kind of notation is also used to denote relationships between entities. For example, in the diagram below there is not necessarily a sales agreement for an accounting point. This is marked by 0..1 at the sales agreement end of the relationship between these two entities. If no multiplicity value is given separately at the end of a connection, the multiplicity will by default be 1.
