ERD is a graphical notation in conceptual data modeling that describes the relationship between storage. ERD is used to model data structures and relationships between data, because it is relatively complex. With ERD we can test the model by ignoring the process that must be done. And with the ERD we try to answer questions such as what data do we need? how the data relate to one another?
ERD using a number of notations and symbols to describe the structure and relationships between data, there are basically three kinds of symbols used are:1. Entity: it is an object that can be identified in the user environment, something that is important for users in the context of a system that will be created. For example customers, workers and others. If A is a worker then A is the content of the workers, whereas if B is a customer then B is the content of the customer. Therefore we must distinguish betweenentitii as a general form and content of a particular description of entities such as A and B in the example above. Entities described in a rectangular shape.Worker2. Attribute: entity has elements called attributes, and functions describing character entities. For example the attribute name of the entity employee workers. Each ERD can have more than one attribute. Entities described in the form of ellipse.3. Relationships: Relationship; as well as the entities in hubunganpun must be distinguished between relationships or other forms of relationships between entities with the contents of the relationship itself. For example in the case of relationships between entities and entity mata_kuliah students is to follow, while the contents of connection can be either nilai_ujian. Relationship depicted in the form of diamonds / diamonds.
The types of relationships: one to one, for example in a company has a rule a driver may only handle one vehicle for some reason.assignment
one to many / many to one, for example, a school has always had the assumption that one class made up of many students but not vice versa, ie a student can not learn in different classes.