information to the elements of the conceptual model. There are also several components in this data model, such as master, operational, and transactional data entities. Physical data model The last one is the physical data model. The physical data model is an extension of the respective logical data model. This data model is usually used to design a database. ERD components After knowing what the data models of ER diagrams are, now we will discuss the components used in creating ER diagrams. In an ERD itself there are four main components for modeling a system. Following are the components. Entity The first is an entity. An entity is a group of objects that can be uniquely identified and different from each other.
This entity is usually depicted
This entity is usually depicted with a rectangular symbol. Then, there is also what is called “Weak Entity”. These weak entities are depicted by a small rectangle within a larger rectangle. Why is it called a weak entity? Because these entities must be directly connected to other entities, because these ws data weak entities cannot be uniquely identified. Attributes Next are attributes. Each entity must have attributes that function to explain or describe the characteristics of that entity. There are several types of attributes commonly used in ERD. Following are the types. Key attributes Key attributes are attributes that function to determine important data. Usually this key attribute is in the form of a number or numeric.
An example of this attribute
is No. KTP, NIM (Student Identification Number), and others. This key attribute is symbolized by an oval circle with the information inside underlined. Simple attributes Next are simple attributes. Simple attributes are attribute Phone Number IR that cannot be further broken down and have a single value. Examples of this attribute are office address, publisher name, and so on. Multivalued attributes Multivalued attributes or Multivalue Attributes are attributes that have more than one attribute value. An example of this attribute is an article website that has several authors. Combined attributes Next are combined attributes or Composite Attributes . A combined attribute is an attribute that consists of several attributes that are smaller in size and have a certain meaning.