Appendix A: Invalid Entity and Attribute Name Components Relationships, A connection or association between entities that represent relevant information Several conventions for defining and naming objects are followed in this manual. all editions of CA ERwin Data Modeler, and includes the following: □ Online and telephone Typographical Conventions. . Entity Relationship Diagram. .. Chapter 5: Naming and Defining Entities and Attributes. 37 .. Attribute Name. An entity–relationship model (ER model for short) describes interrelated things of interest in a In a relational database a relationship between entities is implemented by storing the . they can clutter up a diagram; other diagram techniques often list entity attributes within the Related diagramming convention techniques.
Prefix qualifies Suffix clarifies Using this rule, you can easily validate the design and eliminate many common design problems. If you are tempted to name an attribute "customer-invoice-number," you use the rule to check that the suffix "invoice-number" tells you more about the prefix "customer.
You may sometimes find that it is difficult to give an entity or attribute a name without first giving it a definition. As a general principle, providing a good definition for an entity or attribute is as important as providing a good name.
Naming and Defining Entities and Attributes - CA
The ability to find meaningful names comes with experience and a fundamental understanding of what the model represents.
Since the data model is a description of a business, it is best to choose meaningful business names wherever that is possible. If there is no business name for an entity, you must give the entity a name that fits its purpose in the model.
Synonyms, Homonyms, and Aliases Not everyone speaks the same language. Not everyone is always precise in the use of names. Since entities and attributes are identified by their names in a data model, you need to ensure that synonyms are resolved to ensure that they do not represent redundant data. Then you need to precisely define them so that each person who reads the model can understand which facts are captured in which entity.
It is also important to choose a name that clearly communicates a sense of what the entity or attribute represents.
Naming and Defining Entities and Attributes
Although they can all represent an individual, they have distinct characteristics or qualities. Choose names carefully, and be wary of calling two different things by the same name. For example, if you are dealing with a business area which insists on calling its customers "consumers," do not force or insist on the customer name.
You may have discovered an alias, another name for the same thing, or you may have a new "thing" that is distinct from, although similar to, another "thing. You can enforce unique naming in the modeling environment.
This way you can avoid the accidental use of homonyms words that are written the same but have different meaningsambiguous names, or duplication of entities or attributes in the model. This issue occurs mostly in databases for decision support systems, and software that queries such systems sometimes includes specific methods for handling this issue. The second issue is a 'chasm trap'.
A chasm trap occurs when a model suggests the existence of a relationship between entity types, but the pathway does not exist between certain entity occurrences. For example, a Building has one-or-more Rooms, that hold zero-or-more Computers.
One would expect to be able to query the model to see all the Computers in the Building. However, Computers not currently assigned to a Room because they are under repair or somewhere else are not shown on the list.
Another relation between Building and Computers is needed to capture all the computers in the building. This last modelling issue is the result of a failure to capture all the relationships that exist in the real world in the model. See Entity-Relationship Modelling 2 for details. Entity—relationships and semantic modeling[ edit ] Semantic model[ edit ] A semantic model is a model of concepts, it is sometimes called a "platform independent model".
It is an intensional model. At the latest since Carnapit is well known that: The first part comprises the embedding of a concept in the world of concepts as a whole, i.The Pros and Cons of Attending the Top Three Furry Conventions!
The second part establishes the referential meaning of the concept, i. Extension model[ edit ] An extensional model is one that maps to the elements of a particular methodology or technology, and is thus a "platform specific model".
The UML specification explicitly states that associations in class models are extensional and this is in fact self-evident by considering the extensive array of additional "adornments" provided by the specification over and above those provided by any of the prior candidate "semantic modelling languages".
It incorporates some of the important semantic information about the real world.
Plato himself associates knowledge with the apprehension of unchanging Forms The forms, according to Socrates, are roughly speaking archetypes or abstract representations of the many types of things, and properties and their relationships to one another.
Limitations[ edit ] ER assume information content that can readily be represented in a relational database.
Entity–relationship model - Wikipedia
They describe only a relational structure for this information. They are inadequate for systems in which the information cannot readily be represented in relational form[ citation needed ], such as with semi-structured data. For many systems, possible changes to information contained are nontrivial and important enough to warrant explicit specification.
An alternative is to model change separately, using a process modeling technique.