Database

A database is an organized collection of data stored and accessed.

Note

A large and persistent collection of metadata and data organized in a way that facilitates efficient retrieval and revision.

• Instance: collection stored in a database at a particular moment
• Schema: collection of data and design of it in the database as a whole

Data Models

A collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints.

• Relational Model
• Entity-Relationship Model
• Semi-structured Data Model
• Object-Based Data Model

Data Abstraction

• Physical level: how data are actually stored.

  • Commas to delimit the attributes of a record, special characters to delimit records, how tables are stored in file, etc.

• Logical Level: what data are stored in the database, what are the relationships between those datas.

  • Requirement that the dept name value of an instructor record must appear in the department table is an example of such an interrelationship for example.

• Physical data independence

  • You can change things in the physical metadata and it won’t change anything in the logical metadata.

• Logical data independence

  • Refers to the ability to change the logical schema of a database without it affecting external schemas or application programs that use the database.

Database Design

• Conceptual level
  • Early step in the process of database design where the schema that describes the data and relationships between them is drawn up.

Database Administration

Tasks and responsibility of database administration:

• Management of physical schema
• Assisting with external schema integration
• Maintain ACID properties (Atomicity, Consistency, Isolation, Durability) $\to$ Transactions
• Manage security and reliability
• Loading and reformatting database

Related

• Database System
• DBMS: set of programs to manage the database
  • Data Definition Language
  • Data Manipulation Language