What is Conceptual Database Design?

 The Entity-Relationship Model

• The E-R model employs three basic notions: entity sets, relationship sets, and attributes. 

• An entity is a “thing” or “object” in the real world that is distinguishable from all other objects. An entity may be either concrete, such as a person or a book, or it may be abstract, such as a bank loan, or a holiday, or a concept. 

• An entity is represented by a set of attributes. Attributes are descriptive properties or characteristics possessed by an entity. 

• An entity set is a set of entities of the same type that share the same attributes. For example, the set of all persons who are customers at a particular bank can be defined as the entity set customers.  

• Entity sets do not need to be disjoint. For example, we could define the entity set of all persons who work for a bank (employee) and the entity set of all persons who are customers of the bank (customers). A given person entity might be an employee, a customer, both, or neither. 

• For each attribute, there is a permitted set of values, called the domain (sometimes called the value set), of that attribute. More formally, an attribute of an entity set is a function that maps from the entity set into a domain. Since an entity set may have several attributes, each entity in the set can be described by a set of pairs, one for each attribute of the entity set. 

• A database contains a collection of entity sets.

Definitions

• Entity – an aggregation of a number of data elements – each data element is an attribute of the entity 

• Entity type – a class of entities with the same attributes 

• Relationship – an association between two or more entities that is of particular interest 

What is Conceptual Database Design?

• Process of describing the data, relationships between the data, relationships between the data, and the constraints on the data. 

• After analysis - Gather all the essential data required and understand how the data are related 

• The focus is on the data, rather than on the processes. 

• The output of the conceptual database design is a Conceptual Data Model ( + Data Dictionary)

Gathering Information for Conceptual Data Modeling

• Two perspectives – Top-down 

• Data model is derived from an intimate understanding of the business. – Bottom-up 

• Data model is derived by reviewing specifications and business documents.

Entity-Relationship (ER) Modeling.

• ER Modeling is a top-down approach to database design. 

• Entity Relationship (ER) Diagram – A detailed, logical representation of the entities, associations and data elements for an organization or business

• Notation uses three main constructs 

    – Data entities 

    – Relationships 

    – Attributes 

Chen Model & Crow’s Foot Model