a. Entity: Any thing in the real world with independent existence is called Entity such as an object with physical existence (e.g., car, person, house) or conceptual existence (e.g., a company, job, university course, account, voucher). In the context of above accounting reality, there exist five entities are accounts, vouchers, employees, accounts type and support documents. The accounting data is captured through these entities,
b. Attributes: Attributes are some properties of interest (or characteristics) that further describes the entity such as height, weight and date of birth in case of a person and code and name in case of accounts.
Entity Attributes:
Customer Name, Address, Customer No
Book ISBN, Author, Price
Student Name, Address, Roll No
An entity has value for each of its attributes, which is the data stored in the database.
Attributes may be of several types as follows:
- Composite Vs. Simple attributes
- Single valued Vs. Multi valued
- Store Vs. Derived attributes
- Null values (for absence of data)
- Complex attributes
- Entity types of entity sets
- Value sets of attributes.
c. Relationship : It is a relational database. All entities have bonds (relations) between them.
A relationship is a link between two entities. It tells something about which relationship exists between our entities. For example, vouchers and accounts are related to two ways – vouchers contain debit account(s) and vouchers contain credit account(s).
In ER model those references are represented as explicit relationships rather than attributes. Collection of relationship as called “Relationship Sheet”.
