Database Terminologies

Data

Collection of facts and figures that can be recorded and have implicit meaning.

Name, age, address of people.

Database

A database is a collection of related or connected data that has an implicit meaning. Collection of logically related data stored in an efficient and compact manner.

• It can be generated manually or can be computerised.

Students record data in a university.

DBMS

• Data Base Management System

An application program or system that allows us to create, read, update or delete a database.

Meta-Data

The description and definition of a database stored by DBMS in a category or dictionary.

The number of columns or fields in a relation or the total number of relations.

Constructing a DB

The process of storing data in a database

Manipulating a DB

The retrieval and updating of a database to reflect changes in the mini-world.

‍

I/Os

The cost of reading from the disk to memory

or

The cost of writing from the memory to disk

Query

Used to retrieve data from a database.

Transaction

Used to read or write data into the database.

Database System

The database and the DBMS together constitute a database system.

Database Administrator

Administrates and supervises the database

Responsible for following:

1. Authorizing access to the database.
2. Coordinating and monitoring its use.
3. Keeping a check on software and hardware resources.
4. Efficiency of operations.

Database Designers

Responsible for defining the structure in which the data will be presented and stored in the database. The must communicate with the end users to map out their requirements.

Advantages of Database

• Centralised storage of data (No Redundancy)
• Unauthorised access is denied
• Backup and recovery features
• Integrity constraints
• Multiple views / interfaces
• Flexibility to change data structures
• Persistent storage for program objects

Data Model

It is the logical structure of a database which tells us the operations which could be performed and the integrity constraints to be applied. Data Structure that a database uses to store data.

• Constructs are used to define the database structures

Hierarchical Model, Network Model, Relational Model and many more.

Data Model Operations

These are the operations performed on the data model.

• Basic Model Operations
  • Insert, Delete, Update, Delete
• User-Defined Operations
  • Calculate CGPA, Calculate Annual Tax

Data Model Categories

• Conceptual - High Level, semantics
  • General
  • Entity-based
• Physical - Low Level, internal
  • Details on how data is stored etc.

Database Schema

The description of a database. Includes structure, data types and the constraints. Called Intension

Difference between Data Model and Database Schema

Database State

The actual data stored in a database at a particular moment. AKA instance, occurrence, snapshot Called Extension

Three Schema Architecture

1. Internal Scheme - Internal Level
   1. Describes physical storage structure
   2. Uses a physical data model
2. Conceptual Schema - Conceptual Level
   1. Describes structure for a community of users
   2. Uses conceptual data model or implementation data model
3. External Schema - External Level
   1. Describes various user views
   2. Usually uses the same model as conceptual schema

• Mapping among schemas are needed to process requests.

---

Data Independence

• Logical Data Independence

  • Capacity to change the conceptual schema without having to change the external schema.

• Physical Data Independence

  • Capacity to change the internal schema without having to change the conceptual schema.

Change in internal schema when file structure is reorganised or new indexes are created to improve performance.

When a schema at a lower level is changed only the mappings between this schema and higher level schemas are changed. The higher level schemas themselves are unchanged.

Hence, the application programs need not to be changed.

Database Languages

DDL

• Data Definition Language
• Used by DBA and Database Designers to specify the conceptual schema.
• Can also be used to define external and internal schema in some DBMS.
• In some DBMS, external and internal schema are defined by SDL and VDL

DML

• Data Manipulation Language

• Used to perform data update and retrieval operations

• Can be embedded into a general programming language.

• Types

  • High Level / Non - Procedural Language

    • Specify what data to retrieve
    • Example would be SQL​

  • Low Level / Non - Procedural Language

    • Specify how to retrieve data

SDL

• Storage Definition Language
• Used to define the internal schema

VDL

• View Definition Language
• Used to define the external schema

Database Adapters

A database connector is a software that connects an application to any database. A database adapter is an implementation of a database connector. The connector is more at the conceptual level, while the adapter is at the implementation level, though they refer to the same thing

• Open Database Connectivity (ODBC)

• Java Database Connectivity (JDBC)

DBMS Architectures

• Centralised Architecture

  • Everything resides at a single system such as
    • DBMS, Hardware, Application Program and User Interface