Data Model – SS2 Data Processing Lesson Note (First Term)

Data modelling is the process of structuring and organising data so that it can be implemented in a database management system. A data model describes structured data, such as the data held in relational databases, and may also place constraints on the data stored in its structure. It does not describe unstructured data such as emails or pictures.

Behavioural objectives

By the end of the lesson, students should be able to:

• define data modelling;
• state the difference between structured and unstructured data in relation to data models;
• explain the concepts of data modelling;
• describe data structure and data organisation as the two meanings of the term data model;
• name and describe the conceptual, logical and physical approaches to data modelling.

Why was data modelling developed?

The main effort during the system development life cycle (SDLC) was to produce a set of programs that automate a business process. Processing, rather than data or information, was the key driver for information systems. As the technology and complexity of systems grew, methodologies and modelling techniques were invented. They improved the quality of the deliverables and made sure that inexperienced programmers could follow repeatable SDLC processes.

What is data modelling?

Data modelling is the process of structuring and organising data. The data structures are then typically implemented in a database management system. In addition to defining and organising the data, data modelling may also impose constraints or limitations on data placed within the structure.

Managing large quantities of structured and unstructured data is a primary function of information systems. Data models describe structured data for storage in data management systems such as relational databases. They do not describe unstructured data such as word-processing documents, email messages, pictures, digital audio and video.

What are the concepts of data modelling?

1. Data modelling techniques and tools help to capture and translate complex system designs into easily understood representations of data flows and processes, creating a blueprint for construction and re-engineering.
2. Data models provide a structure for data used within the information system by providing a specific definition and format.
3. The data model shows the data flow and logical interrelationship among different data elements.
4. Compatibility of data can be achieved if a data model is used consistently across the systems.

The term data model refers to two different things: a description of data structure and the way data is organised using the database management system (DBMS).

Data structure

A data model describes the structure of the data within a given domain and, by implication, the underlying structure of that domain itself.

Data organisation

A data model also describes how to organise data using a database management system.

What are the approaches to data modelling?

There are different approaches to data modelling, including:

1. Conceptual data modelling: This identifies the highest-level relationships between different entities. It is the first step in organising the data requirements.
2. Logical data modelling: This illustrates the specific entities, attributes and relationships involved in a business function. It serves as the basis for the creation of the physical data model.
3. Physical data modelling: This represents an application and database-specific implementation of a logical data model and describes the physical means used to store data.

Evaluation

1. Define data modelling.
2. Give three examples of unstructured data that a data model does not describe.
3. State two concepts of data modelling.
4. Which approach to data modelling is the first step in organising data requirements?
5. Explain how logical data modelling is related to physical data modelling.

Assignment

1. Explain the two meanings of the term data model.
2. Describe the conceptual, logical and physical approaches to data modelling in your own words.