Who invented er diagram

In the Chen notation, a partial participation is represented by a single line. The relationship shown above means that each student, without exception, must be guided by one chosen professor, and one — but not every — professor can guide many students. So there is no student that is not guided by a professor, and on the other hand there can be professors who don't guide any students. In the Chen notation, we distinguish types of entities : entity weak entity — an entity that cannot be uniquely identified by its attributes alone.

We underline the discriminator with a dashed line: multivalued attribute — an attribute that can have many values there are many distinct values entered for it in the same column of the table. In the Chen notation, this attribute is represented by dashed oval: For example, having given the price excluding VAT and the VAT rate, we can calculate the price including VAT: Some attributes can be further subdivided into smaller parts.

In the mid s, when faced with a need to translate strategic business requirements into something useful to the world of information systems, Finkelstein formulated the concepts and modeling notation that became the basis of information engineering.

He wrote a series of articles entitled Information Engineering that saw publication in in Computerworld magazine. Finkelstein is also a champion of John Zachman and currently provides training and consulting in the Zachman Framework, focusing on rapid business reengineering. He began his technology career in for IBM. In the s, Martin became known as the rare sort of individual considered a guru in both the technology and business worlds. As mentioned earlier, in Martin teamed up with Clive Finkelstein on their seminal report for the Savant Institute, Information Engineering.

For Martin, the CASE process needed to provide the ability to automate defining a data dictionary or Metadata encyclopedia directly from the description of a business process. The key attribute is represented by an ellipse with the text underlined. An attribute that composed of many other attributes is known as a composite attribute.

The composite attribute is represented by an ellipse, and those ellipses are connected with an ellipse. An attribute can have more than one value. These attributes are known as a multivalued attribute. The double oval is used to represent multivalued attribute. An attribute that can be derived from other attribute is known as a derived attribute.

It can be represented by a dashed ellipse. For example, A person's age changes over time and can be derived from another attribute like Date of birth. A relationship is used to describe the relation between entities. Diamond or rhombus is used to represent the relationship. When only one instance of an entity is associated with the relationship, then it is known as one to one relationship.

For example, A female can marry to one male, and a male can marry to one female. When only one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then this is known as a one-to-many relationship.

For example, Scientist can invent many inventions, but the invention is done by the only specific scientist.

When more than one instance of the entity on the left, and only one instance of an entity on the right associates with the relationship then it is known as a many-to-one relationship. For example, Student enrolls for only one course, but a course can have many students. When more than one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then it is known as a many-to-many relationship.

For example, Employee can assign by many projects and project can have many employees. JavaTpoint offers too many high quality services. Mail us on [email protected] , to get more information about given services.

Please mail your requirement at [email protected] Duration: 1 week to 2 week. In addition to collecting data types into user-defined data types, many of the object databases allow for the creation of extensions to the base table types. These extensions may be used to embed additional information into an object or they may be used to establish relationships to other objects.

In addition the extensions may be used to create "aggregate" objects that consist entirely of data inside other objects. These data type extensions fall into several categories:. Data extensions with user-defined data types. Lists of repeating data items Lists of groups of repeating data items Pointer extensions to data types. Single pointers to other rows Lists of pointers to other rows Lists of pointers to pointers to other rows A pointer to another whole table List of pointers to other whole tables As we can see, we are presented with a mind-boggling array of choices of data structures.

There are, however, certain rules that the database designer can follow when choosing a data structure to implement within their model. While each of these methods are fully discussed within Chapters 5 through Chapter 8, let's begin our journey by talking about how these data structures are represented graphically in our design documentation.