Konsep Basis Data

Basis Data

Database atau basis data adalah kumpulan informasi yang disimpan di dalam komputer secara sistematik sehingga dapat diperiksa menggunakan suatu program komputer untuk memperoleh informasi dari basis data tersebut. Kegunaan utama sistem basis data adalah agar pemakai mampu menyusun suatu pandangan (view) abstraksi data.

Database-System Applications

- Enterprise Information : Sales, accounting, human resources, manufacturing

- Banking and Finance : Banking, credit, finance

Database System vs File Processing System

- Data redudancy & inconsistency

- Difficulty in accessing data

- Data isolation

- Integrity problems

- Atomicity problems

- Concurrent-access anomalies

- Security problems

Data Abstraction

- Physical Level

- Logical Level

- View Level

Relational Database

- Uses a collection of tables to represent both data and the relationships among those data

- Each table has multiple columns, and each column has a unique name

- Tables are also known as relations

- Record-based models are so named because the database is structured in fixed-format records of several types

- Each table contains records of a particular type. Each record type defines a fixed number of fields, or attributes

- The columns of the table correspond to the attributes of the record type

- The relational data model is the most widely used data model, and a vast majority of current database systems are based on the relational model

Order of the Tuples

- The order is irrelevant

- Because a relation is a set of tuples

- And also could be sorted by query and index

Attribute Types

- The set of allowed values for each attribute is called the domain of the attribute

- Attribute values are (normally) required to be atomic; that is, indivisible

- The special value null is a member of every domain

- The null value causes complications in the definition of many operations

Database Schema

- Database schema : logical design of the database

- Database instance : snapshot of the data in the database at a given instant time

Keys

- Must have a way to specify how tuples within a given relation are distinguished

- Expressed in terms of their attributes

- The values of the attribute values of a tuple must be such that they can uniquely identify the tuple

- No two tuples in a relation are allowed to have exactly the same value for all attributes