Entity Relationship Modelling
Conceptual Data Model
A systems analyst designing a new system would need to produce a conceptual data model describing how data needs to be stored - how elements within the data are related. A conceptual data model is independent of any software that may be used for implementation.
The following key terms are used,
- Entity - an object, event or person about which data is stored.
- Attribute - a property or charactristic of an entity - like a field within a table
- Relationship - a link or association between entities.
- Degree of Relationship - the nature of the relationship between two entities
Eg. husband - wife
Eg. parent - children, customer - order, sport - team, team - result
Eg. student - course, film - film star
You can also have a Many-To-One relationsip between entities. The arrows would be the mirror of the One-To-Many diagram.
The data requirements for a database of school sports results are as follows.
A number of sports are played in the school. Each sport has a different name. A number of teams play each sport. Each team has a different name (eg U14A etc). The results of each match are to be stored including the date, points for and against, the result and the opposition.
Suggest 3 entities, listing their attributes. Suggest which attribute(s) in each entity will uniquely identify the records stored. Draw an entity relationship diagram to show the relationship between the entities.
Draw Entity Relationship Diagrams To Illustrate the Relationships
- Employee - Company Car
- Ward - Patient
- Album - Singer
- Product - Component
- Homeowner - Main Residence
- Racehorse owner - Racehorse