Entity Relationship Model

King Fahd University of Petroleum and Minerals

Department of Information and Computer Science

ICS 334: Database Systems

Fall 2000-2001

Date: 27th September 2000 Assignment # 1: The Entity Relationship Model Due date: 7th October 2000

Written Part

Problem 2.1 PP 69 (5 Points)

Data independence refers to the concepts of isolating the data that are seen by particular users from their representations in the physical storage. It is very important that whatever changes are made in the physical level it should not affect the conceptual level and whatever changes are made to the conceptual level it should not affect the users level.

Problem 2.3 PP 69 (9 Points)

A data model is an integrated collection of concepts for describing data, relationships between data and constraints on the data in an organization. There are three types of data models:

1. Object-based data model: uses concepts such as entities, attributes and relationships. Some of the common types of object-based data models are: Entity-Relationship, semantic, functional and Object-Oriented.

2. Record-based data model: in which the database consists of a number of fixed-format records of possibly differing types. Each record type defines a fixed number of fields each typically of fixed length. Examples are relational, network and Hierarchical data models

3. Physical data models: describe how data is stored in the computer, representing information such as record structure, record orderings, and access paths. The most common physical data models are unifying model and frame memory.

Problem 3.2 PP 109 (6 Points)

The candidate key is an attribute, or a set of attributes that uniquely identifies tuples of the relation while no subset of it can be a candidate key. A primary key is the candidate key that is selected to identify tuples and be the main key.

A foreign key is an attribute, or a set of attributes, within one relation that matches the candidate key of some...