# Chens notation for entity relationship modeling clay

### Entity–relationship model - Wikipedia

Pin-Shan Chen: The Entity Relationship Model - Toward a Unified View of Data (Reprint). .. Peter P. Chen, R. Clay Sprowls: Proceedings of. models, logical geographic models, Entity-Relationship Model, Object Modeling The models we compare are: (a) ER (Chen, ), as a representative of the modelled as a function from space to the set (sand, clay, }. . The symbol representing a class has three areas: The upper area contains the class name. ER Diagram Notation. E-R Diagram: Chen Model. Entity. represented by a rectangle with its name in capital letters. Relationships. represented by an active or.

## Chen ERD - Draw entity relationship diagrams (ER diagrams) easily with Edraw!

In the Chen notation, this attribute is represented by dashed oval: Some attributes can be further subdivided into smaller parts. These are called composite attributes and are depicted as follows: Two kinds of relationship are distinguished: A strong relationship is represented by a single rhombus: This relationship is represented by a double rhombus: N The customer may place many orders, but each order can be placed by one customer only: N One student may belong to more than one student organizations, and one organization can admit more than one student: Participation constraints An entity set may participate in a relation either totally or partially.

Total participation means that every entity in the set is involved in the relationship, e. In the Chen notation, this kind of relation is depicted as a double line.

Partial participation means that not all entities in the set are involved in the relationship, e. In the Chen notation, a partial participation is represented by a single line. 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".

### ERD Notations in Data Modeling. Part 2 – Chen Notation

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 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".

## Entity–relationship model

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.

Competency 2.4 Entity Relationship Modeling ITSE 2309

Limitations[ edit ] ER assume information content that can readily be represented in a relational database. 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.

### Chen ERD - Draw entity relationship diagrams (ER diagrams) easily with Edraw!

An alternative is to model change separately, using a process modeling technique. Additional techniques can be used for other aspects of systems. For instance, ER models roughly correspond to just 1 of the 14 different modeling techniques offered by UML.

Even where it is suitable in principle, ER modeling is rarely used as a separate activity. One reason for this is today's abundance of tools to support diagramming and other design support directly on relational database management systems.