1.1. Context of Database Systems

Concurrency-control manager

It controls the interaction among the concurrent transactions, to ensure the consistency of the database.

Transaction-management component

It ensures that the database remains in a consistent (correct) state despite system failures.

Query Evaluation Engine

It executes low-level instructions generated by the DML compiler.

DDL interpreter

It interprets DDL statements and records the definitions in the data dictionary.

Transaction

It is a collection of operations that performs a single logical function in a database application.

Modern database system

It is a complex software system whose task is to manage a large, complex collection of data.

Database Administrator

It is a person who has central control over the system.

Storage Manager

It is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.

View of Data

It is an architecture for a database system.

SQL Query Language

It is nonprocedural.

Instances and Schemas

It is similar to types and variables in programming languages.

Physical Data Indepedence

It is the ability to modify the physical schema without changing the logical schema.

Instance

It is the actual content of the database at a particular point in time.

Data Manipulation Language

It is the language for accessing and updating the data organized by the appropriate data model.

Logical Schema

It is the overall logical structure of the database.

Physical Schema

It is the overall physical structure of the database.

1. Procedural DML 2. Declarative DML

Two types of data-manipulation language

Declarative DML

What are usually easier to learn and use? Procedural DML or Declarative DML?

Client server

One server machine executes work on behalf of multiple client machines.

1. Data redundancy and inconsistency 2. Difficulty in accessing data 3. Data isolation 4. Integrity problems 5. Atomicity of updates 6. Concurrent access by multiple users 7. Security problems

Purpose of Database Systems:

Two-tier architecture

The application resides at the client machine, where it invokes database system functionality at the server machine.

Data Models

These are collection of tools for describing data, data relationships, data semantics, and data constraints.

Application programs

These are programs that are used to interact with the database in this fashion.

Database Systems

These are used to manage collections of data that are highly valuable, relatively large, and accessed by multiple users and applications, often at the same time.

Data files

These store the database itself.

Indices

They can provide fast access to data items.

DBMS

This contains information about a particular enterprise: 1) Collection of interrelated data; 2) Set of programs to access the data; 3) An environment that is both convenient and efficient to use.

Relational Model

This is when all the data is stored in various tables.

Data dictionary

This stores metadata about the structure of the database, in particular the schema of the database.

Data Dictionary

DDL compiler generates a set of table templates stored in ?

Query Language

DML is also known as ?

Metadata

Data dictionary contains what?

1. Enterprise Information 2. Manufacturing 3. Banking and Finance 4. Universities 5. Airlines 6. Telecommunication 7. Web-based Services 8. Document Databases 9. Navigation Systems

Database Applications Example:

Logical Design

Deciding on the database schema.

Physical Design

Deciding on the physical layout of the database.

Distributed databases

Geographical distribution, schema/data heterogeneity

Query Language

It is the portion of a DML that involves information retrieval.

Data Definition Language (DDL)

It is the specification notation for defining the database schema.

Database index

It provides pointers to those data items that hold a particular value.

Procedural DML

It requires a user to specify what data are needed and how to get those data.

Declarative DML

It requires a user to specify what data are needed without specifying how to get those data.

Databases

It touches all aspects of our lives.

DML compiler

It translates DML statements in a query language into an evaluation plan consisting of low-level instructions that the query evaluation engine understands.

Parallel databases

Many core shared memory, shared disk, shared nothing.

Centralized databases

One to a few cores, shared memory

Three-tier architecture

The client machine acts as a front end and does not contain any direct database calls.

1. The storage manager 2. The query processor component 3. The transaction management component.

The functional components of a database system can be divided into:

1. DDL interpreter 2. DML compiler 3. Query evaluation engine

The query processor components include:

1. Data files 2. Data dictionary 3. Indices

The storage manager implements several data structures as part of the physical system implementation: