Essay on Qwertyttter

2667 Words Oct 19th, 2014 11 Pages
COMM 226 Database Systems
INTRODUCTION A database is a structured collection of data, and is usually stored electronically to facilitate computerassisted search and retrieval. The electronic format allows different users to have views of the data that serve their particular needs. Furthermore, the database management software can ensure the consistency, integrity, and security of the database, provided the data needs of the organization have been correctly modeled and implemented. DATA MODELING Although the field of information systems engineering is young relative to most other engineering disciplines, it does apply formal modeling methods to study and predict aspects of a planned system. Different kinds of models may exhibit the user
…show more content…
The ERD not only includes entities and relationships but also may include a set of attributes that describes each entity and identifies primary and foreign keys. ENTITIES Entities are concepts within the ERD model. Each entity is represented by a box within the ERD. An entity represents a separately identifiable subject of interest to the enterprise, typically a person, place, thing, or event. An entity might be considered a container that holds all of the instances of a particular thing in a system. Entities are equivalent to database tables in a relational database, with each row of the table representing an instance of that entity. Remember that each entity represents a container for instances of the thing in question. The diagram below has an entity for student and another for school. This indicates that the system being modeled may contain one or more students and one or more schools.

COMM 226 Database Systems
There are several notations to represent ERD diagrams as indicated in the diagram below. The most popular notation is Crow’s foot as it is supported by many popular software tools.

RELATIONSHIPS Relationships are represented by lines between entities. Relationship lines indicate that each instance of an entity may have a relationship with instances of the connected entity, and vice versa.

The diagram above now indicates that students may have some relationship with schools. More specifically, there may be a

Related Documents