data modeling

This content is an extract from GetAhead in Business Analysis - the FULL course is in eBook and multimedia CD-Rom format.

data modeling
The success of any enterprise relies on the efficient flow and processing of information. In this example information flows around the various departments within the organization. This information can take many forms, for example it could be written, oral or electronic. The general manager regularly communicates with staff in the sales and marketing and accounts departments by using e-mail. Orders received by sales and marketing are forwarded to the production and accounts departments, for fulfillment and invoicing. The accounts department forward regular written reports to the general manager, they also raise invoices and send these to the customers.

Data modeling is a technique aimed at optimizing the way that information is stored and used within an organization. It begins with the identification of the main data groups, in this example the invoice (sent from the accounts department to the customers) and continues by defining the detailed content of each of these data groups. This results in structured definitions for all of the information that is stored and used within a given system.

Entities & Relationships.
Data modeling uses a standard set of symbols to represent each of these defined data groups and then proceeds by establishing the relationships between them. The first of these symbols is the soft-box entity symbol. An entity is something about which data will be stored within the system under consideration.
In this example the data group invoice has been identified as a system entity. The other main component on a data model is the relationship line. A Relationship is an association between two entities to which all of the occurrences of those entities must conform. The relationship is represented by a line that joins the two entities, to which it refers.

This line represents two reciprocal relationships: That of the first entity with respect to the second; and that of the second entity with respect to the first.
Data modeling is all about identifying entities and their relationships and then drawing a diagram that accurately depicts the system. This applies equally to the design of a new system or the analysis of an existing one. The end result of data modeling should be a clear picture of how information is stored and related within a proposed, or existing, system. The technique provides a solid foundation for systems design and a universal standard for system documentation. Data modeling is an essential precursor to analysis & design, maintenance & documentation and improving the performance of an existing system.

Defining Entities.
Some examples of information systems and their entities are shown on this page: An entity is represented by a box containing the name of that entity.
This course uses symbols that are standard in the IT industry. This uses the soft-box symbol shown to represent an entity. If an organization uses a different symbol set, this is not a problem, as data modeling techniques are the same regardless of the symbols being used. A clear cut definition of entity is not really possible, they even vary in nature. For example, in the airline system, whilst an aircraft is a physical object (entities often are) a flight is an event and an airport is a location. However entities are nearly always those things about which data will be stored within the system under investigation. Note that entities are always named in the singular; for example: Customer, Account and Loan, and not Customers, Accounts and Loans.

Entity Types.
Similar entity occurrences are grouped together and collectively termed an entity type. It is entity types that are identified and drawn on the data model. An entity occurrence identifies a specific resource, event, location, notion or (more typically) physical object. In this course the term 'entity' is, by default, referring to entity type. The term entity occurrence will be specifically used where that is relevant. Each entity has a data group associated with it. The elements of the data group are referred to as the 'attributes ' of the entity. The distinction between what is an attribute of an entity and what is an entity in its own right is often unclear. This is illustrated shortly.

This content is an extract from GetAhead in Business Analysis - the FULL course is in eBook and multimedia CD-Rom format. TOP