Data Flow / Entity Description

Data Flow Diagrams:

Data Flow Diagrams are used to represent the functions that an organization performs. These diagrams decribe the flow information between processes, entities and data stores and are shown in the legend below.

The data that is passed can be tangible (a report) or intangible (expected length of stay). The flow of data between process is shown by an arrow. A flow into a process is called an input, while the flow out of a process is called an output. Data can be passed to and form proccess, data stores, or entities.

Data stores are structured repositories of information. The information can be stored in a physical format, such as in filing cabinets, or in a logical format such as in a database.

Entities are persons, places or things. These are usually the initiators of information, or the final resting place of information.

A process is the sequence of steps that transforms information. Processes may be automated through the use of computers, manual, or a combination of both. In systems modelling, a process serves the same purpose as a verb in the English language; they perform an action. As verbs have a definition in a dictionary, processes have a set of descriptive attributes.

i.e. The Add Ward process has the following descriptive attributes:

Description: Identify the layout of the hospital.
Inputs: Ward #, description, number of rooms.
Outputs: Ward information.
Prompts: Enter ward information.
Errors: Ward is already on the sytem.

ENTITY RELATIONSHIP DIAGRAMS

Entity relationship diagrams are used to represent the information used in a an organization at a conceptual level. The diagram describes the entities and their relationships.

An entity is a collection of information that describes an important concept within an organization. The concepts described may be tangible (a piece of equipment) or intangible (a schedule). Entities, in systems modelling, serve the same purpose as nouns in the English language, they describe a person, place or thing. As nouns have a definition in a dictionary, entities have a set of descriptive attributes.

i.e.: A Ward is described by the following attributes:

Definintion: Contains description of the wards.
Attributes: ward #, description, # rooms
Identifiers: ways of identifying a ward
Constraints: restrictions placed on the ward
Dimensions: the expected size of the entity

Entities are related to other entities, in the context of an organization, if there is a requirement to associate items for comparison or reporting purposes. A relation between entities is shown with a connecting arrow. Different types of arrows are used for each type if relationship (see the legend below)

Example:

A Ward is associated with rooms because there is a need to identify a room according to the speciality of the ward to be able to assign patients and schedule staff. The diagram is read as follows: "One ward has one or more rooms."

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Data Flow / Entity Description

Data Flow Diagrams:

ENTITY RELATIONSHIP DIAGRAMS

Last Modified Mar. 5, 1996 by Darrell Nash

Last Modified Mar. 5, 1996 by
Darrell Nash