Ch 6Database Concepts — Class 11 Informatics Practices, concept-first.

Data is valuable only if it can be stored, found, updated and summarised without error. Having seen why data matters, the natural next question is how to keep it — and the answer this chapter builds t…

Every program that shows you information — a report on a website, a bill at a shop counter — has to read that information from somewhere on the computer.

A file system serves a school or an office well enough while the data is small. The trouble starts as the number of files increases and the volume of data grows — the arrangement becomes progressively…

Each limitation of the file system traces back to one root: files hold data but do not relate or manage it.

A file system stores each department's data in its own separate file; a database stores all of it in one place as a set of related tables.

Managing data efficiently with a DBMS requires a small vocabulary of core ideas. Each term below answers a different question about a database: what is its design (schema), what data is allowed in (co…

Every DBMS is built on some underlying data model — a description of how the database is structured: how data are defined and represented, what relationships exist among the data, and what constraints…

A relation looks like an ordinary table, but it is not merely a table — the relational data model binds it with rules that a data file or a simple table never has to obey.

The relational model insists that the tuples within a relation be distinct: no two rows of a table may carry the same values for all their attributes.

A relation may contain not one but several attributes whose values are always distinct — and any one of them, on its own, is enough to uniquely identify the tuples.

Every tuple in a relation must be distinguishable from every other — the relational model requires at least one attribute whose values are unique and never NULL, so that each row can be picked out wit…

Sometimes a relation offers no single attribute that can tell all its tuples apart — every individual column contains repeated values.

A primary key identifies tuples within one relation; a foreign key is what ties two relations together.

- A file in a file system is a container used to store data in a computer; data files can be created, searched, modified and deleted, but each file stands on its own.