Understanding Relational Databases and Entity-Relationship Diagrams, Slides of Business Administration

Download Understanding Relational Databases and Entity-Relationship Diagrams and more Slides Business Administration in PDF only on Docsity! Relational DBs: • Data items stored in tables • Specific fields in tables related to other field in other tables (joint) • infinite number of possible viewpoints on the data (queries) • Highly flexible DB but overly slow for complex searches • Oracle, SyBase, Ingres, Access, Paradox for Windows... Docsity.com Describing relationships • Attempt at modelling the business elements (entities) and their relationships (links) • Can be based on users’ descriptions of the business processes • Specifies dependencies between the data items • Coded in an Entity-Relationship Diagram (ERD) Docsity.com Entity Relationship Diagram Docsity.com Example 2 – Sales Order Processing • Entities • Relationships • Use a business object based approach? Docsity.com Next step - creating the data structure • Few rules - a lot of experience • Can get quite complex (paramount for the speed of the DB) • Tables must be normalised - ie redundancy is limited to the strict minimum by an algorithm • In practice, normalisation is not always the best Docsity.com Normalisation • Process of simplifying the relationships amongst data items as much as possible (see example provided - handout) • Through an iterative process, structure of data is refined to 1NF, 2NF, 3NF etc. • Reasons for normalisation: – to simplify retrieval (speed of response) – to simplify maintenance (updates, deletion, insertions) – to reduce the need to restructure the data for each new application Docsity.com First Normal Form • design record structure so that each record looks the same (same length, no repeating groups) • repetition within a record means one relation was missed = create new relation • elements of repeating groups are stored as a separate entity, in a separate table • normalised records have a fixed length and expanded primary key Docsity.com