Question 4

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4. Data Flow & Entity Relationship Diagrams

The Main Components of an Entity Relationship Diagram

Entity Relationship Diagrams are the top-down planning of data to identify the following 3 components:

Entities involved - entities are something real or abstract which we store data about (e.g. the site, engineer)

Attributes of those entities - attributes are basic units of information which describe an entity (e.g. name)

Relationships among them to show how they are related.\

Types of Entity Relationships

One and only one

Zero or one

One or multiple

Zero, one or multiple

More than one

Differences Between IDEFO Technique & Data Flow Modelling

Data Flow Diagrams (DFDs)

Introduced in 1960s by IBM as a structured approach to systems analysis to develop software.

Was developed in 1970s by others such as DeMarco, Gane and Sarson.

They are a network representation of a system through which complex process are decomposed into sub-processes in a top-down approach.

When a process is broken down, the main process if called the 'parent' whilst the sub-processes are called the 'child.

Inputs and outputs of a child diagram must be the same as the associated parent diagram - this is known as balancing of DFDs.

Are user friendly, easy to learn, read and use and allow each member of the organisation to read their relevant level.

IDEFO Technique

The Integrated Computer Aided Manufacture Definition Method.

Is an automated graphical adaption of Structured Analysis & Design Technique aimed at standardising contractor communications & services.

Developed by US Air Force in early 1970s to standardise the manufacturing process description across many different aerospace contractors.

The IEDO models adopt a hierarchical approach which is based upon activities which are represented by a box, which under control, transfers inputs into outputs using a mechanism.

Similarities Between Techniques

Both adopt a hierarchical approach where activities or processes can be broken down.

The balancing and consistency rules apply to both and must be maintained between the parent & child diagrams.

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