Database Management System Lecture 3 Models of Database Management Systems
Learning Outcome • Compare and contrast the structure of different database management systems • Define hierarchical databases • Define network databases • Define relational databases • Define object-oriented databases
Hierarchical Databases • The hierarchical data model organizes data in a tree structure (as shown in the Figure) which includes parents and child data segments.
Hierarchical Databases (Cont.) • Hierarchical databases were introduced by IBM in the 1960s with the introduction of their IMS DBMS and were popular until the 1970s • It is one of the oldest methods of organizing and storing data
Hierarchical Databases (Cont.) • A hierarchical database is organized in pyramid fashion, like the branches of a tree extending downwards • Related fields or records are grouped together so that there are higher-level records and lower-level records
Network Databases Model (Cont) • The network data model was formally defined in 1971 at the Conference on Data Systems Languages (CODASYL). • It is a modified version of the hierarchical model described with the one-to-many parent-child relationship constraint relaxed allowing many-to-many relationships in data
Network Databases Model (Cont) • a network database looks more like a cobweb or interconnected network of records • child or member can have more than one parent (or owner).
First Generation DBMS: Network and Hierarchical • Required complex programs for even simple queries. Minimal data independence
Relational Data Model (Cont.) • The most widely used data model in DBMSs • It was developed by E. F. Codd at IBM in 1970. • Data in a relational data model is organised in tables. • Each table is composed of a collection of records.
Relational Data Model (Cont.) • Each record contains a set of fields. • Tables in a database can have relationships between them. • Each row in a table is unique with no two rows or more having the same values in all its fields
Relational Data Model (Cont.) • Tuple / Row • A single row in the table is called as tuple. Each row represents the data of a single entity. • Attribute / Column • A column stores an attribute of the entity. For example, if details of students are stored then student name is an attribute; course is another attribute and so on.
Relational Data Model (Cont.) • Column Name • Each column in the table is given a name. This name is used to refer to value in the column • Table Name • Each table is given a name. This is used to refer to the table. The name depicts the content of the table
Object-oriented Databases (OODBMS) (Cont.) • An OODBMS is the result of combining object oriented programming principles with database management principles. .
Object-oriented Databases (OODBMS) (Cont.) • One-to-one mapping between object-oriented programming objects and database objects is achieved in OODBs. • Thus, less overhead can be achieved when storing and retrieving database objects by object-oriented applications
Object-oriented Databases (OODBMS) (Cont.) • able to handle many new data types, including graphics, photographs, audio, and video • an object-oriented database can be used to store data from a variety of media sources, such as photographs and text, and produce work, as output, in a multimedia format.
Object-oriented Databases (OODBMS) (Cont.) • Object-oriented databases use small, reusable chunks of software called objects • The objects themselves are stored in the object-oriented database
Object-oriented Databases (OODBMS) (Cont.) • Each object consists of two elements: 1) a piece of data (e.g., sound, video, text, or graphics) 2) the instructions, or software programs called methods, for what to do with the data
Object-oriented Databases (OODBMS) (Cont.) • The instructions contained within the object are used to do something with the data in the object • For example, test scores would be within the object as would the instructions for calculating average test score
Object-oriented Databases (OODBMS) (Cont.) • Object-oriented databases have two disadvantages • they are more costly to develop 2) most organizations are reluctant to abandon or convert from those databases that they have already invested money in developing and implementing
Object-oriented Databases (OODBMS) (Cont.) • benefits to object-oriented databases are • The ability to mix and match reusable objects provides incredible multimedia capability • Healthcare organizations, for example, can store, track, and recall CAT scans, X-rays, electrocardiograms and many other forms of crucial data.
Summary • In this lesson, the following topics were discussed: • Compare and contrast the structure of different database management systems. • Define hierarchical databases. • Define network databases. • Define relational databases. • Define object-oriented databases.