Data Model II: Types of Data Modelling – SS2 Data Processing Lesson Note (First Term)

A data model is the way a database organises its data. The six types in this lesson are the flat model, hierarchical model, network model, relational model, object-relational model and star schema. Each one arranges data differently, for example in a single table, a tree, records linked by sets, or fact tables linked to dimension tables.

Behavioural objectives

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

• name the six types of data modelling;
• describe the flat, hierarchical and network models;
• explain the relational and object-relational models;
• state what a star schema is and what it consists of.

What are the types of data modelling?

Flat model

The flat model (or table model) consists of a single, two-dimensional array of data elements. All members of a given column are assumed to be similar in values, and all members of a row are assumed to be related to one another.

Hierarchical model

In a hierarchical database, data is organised into an upside-down tree-like structure. Each record has a single upward link to describe the nesting, and a sort field keeps the records in a particular order in each same-level list. Hierarchical structures were widely used in the early mainframe database management systems.

Network model

This model organises data using two fundamental constructs, called records and sets. Records contain fields, and sets define one-to-many relationships between records: one owner, and many members.

Relational model

The relational model, or relational database model, is based on first-order predicate logic. Its core idea is to describe a database as a collection of predicates over a finite set of predicate variables, describing constraints on the possible values and combinations of values.

Object-relational model

The object-relational model is similar to the relational database model, but objects, classes and inheritance are directly supported in database schemas and the query language. An object-relational database can be said to provide a middle ground between relational databases and object-oriented databases (OODBMS).

Star schema

The star schema is the simplest style of data warehouse schema. It consists of a few “fact tables” (possibly only one, justifying the name) referencing any number of dimension tables. The star schema is considered an important special case of the snowflake schema.

Evaluation

1. List the six types of data modelling.
2. Describe how data is arranged in a flat model.
3. In the network model, what are records and sets?
4. How is the object-relational model similar to the relational model, and what does it add?
5. What does a star schema consist of?

Assignment

Explain the hierarchical model and the network model in your own words. State one difference between them.