8.5: Concise Summary

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SQL, a non-procedural query language, is a major database management system that helps organize and log data. Commands and clauses like CREATE, SELECT, etc. are what makes SQL work and gives it functionality. Using these commands and clauses, it is possible to create databases, create tables, edit data within tables, add columns and rows, create keys and so on.

The intuitive words and language that make up these tables allow people who may not be skilled in computer science to be able to use the system. Some of the commands are powerful in another sense as well: they allow the user to quickly scan through all of the given information and return only a specific set based on any number of parameters that the user decides are necessary.

Using other commands, data can be linked between two tables, using characteristics such as Referential Integrity, primary keys, and foreign keys. Primary keys uniquely identify records in tables, while the foreign keys reference the primary key. The linking that results from this is called a relationship. Referential integrity helps prevent the duplication of already existing data and it helps make sure that necessary records aren’t accidently deleted. Referential integrity gives SQL a way to make sure that the data that is in the table is correct and updated due to constraints on what can be changed, and who it can be changed by. The many features of SQL enable it to be the most popular query language in the world.

Furthermore, this module discusses the process of transforming a data model into a database design as various aspects of data models and designs, how they relate to each other, and how they relate to the systems analysis and design process in general and to the systems development life cycle (SDLC) in particular. Transforming a data model into a database design requires three major tasks: replacing each entity with a table and each attribute with a column, representing relationships and maximum cardinality by placing foreign keys, and representing minimum cardinality by defining actions to constrain activities on values of primary and foreign keys.

Four uses for ID-dependent entities are N:M relationships, association relationships, multivalued attributes, and archetype/instance relationships. An association relationship differs from an intersection table because the ID-dependent entity has no key data. In all ID-dependent entities, the key of the parent is already in the child