Database Systems: Introduction

• Chapter 1 is an introduction to database systems.
• Covers the purpose of database systems, data models, and the overall system structure

Database Management Systems

• A DBMS is a collection of interrelated data which helps in accessing the data efficiently.
• It contains data about a particular enterprise.
• DBMS provides a convenient and efficient environment for users.
• Common database applications include banking, airlines, universities, sales, manufacturing, and human resources.
• Databases impact nearly all aspects of life.

Purpose of Database Systems

• Early database applications were built on top of file systems.
• Drawbacks of using file systems to store data include: data redundancy and inconsistency and difficulty in accessing data.
• More drawbacks: data isolation, integrity problems, atomicity of updates, concurrent access by multiple users, and security.
• Issues from concurrent access: Uncontrolled concurrent accesses can lead to inconsistencies.
• Database systems resolve many of the problems associated with file systems.

Levels of Abstraction

• Physical level describes how a record is stored.
• Logical level describes data stored in the database and the relationships among the data.
• View level application programs hide details of data types.
• Views can hide information for security purposes.

View of Data

• A database system architecture has multiple levels of abstraction for different views of data.
• The levels are view level, logical level, and physical level.

Instances and Schemas

• Schemas are the logical structure of the database.
• Schemas are similar to types and variables in programming languages.
• An instance is the actual content of the database at a particular point in time.
• Analogous to the value of a variable.
• Logical schema refers to the database design at the logical level.
• Physical schema refers to the database design at the physical level.
• Physical data independence is the ability to modify the physical schema without changing the logical schema.

Data Models

• A data model is a collection of tools for describing data, data relationships, data semantics, and data constraints.
• Common models include the Entity-Relationship, Relational, Object-oriented, and Semi-structured data models
• Older models include the network model and hierarchical model.

Entity-Relationship Model

• The Entity-Relationship (E-R) model represents the real world in terms of entities (objects) and relationships between entities.
• This is widely used for database design.
• Database design in E-R model is usually be converted to design in the relational model that is used for storage and processing

Relational Model

• Tables of data with rows representing records and columns representing attributes
• The relational model is used for storage.

Data Definition Language

• Data Definition Language (DDL) is a specification notation for defining the database schema.
• A DDL compiler generates a set of tables stored in a data dictionary.
• The data dictionary contains metadata (data about data) which includes database schema and data storage and definition language.
• The data storage and definition language is a language in which the storage structure and access methods used by the database system are specified.
• The language is usually an extension of the data definition language

Data Manipulation Language

• Data Manipulation Language (DML) is a language for accessing and manipulating the data that is organized by the appropriate data model.
• DML is also known as query language.
• Classes of languages include Procedural and Nonprocedural.
• Procedural specifies what data is required and how to get those data.
• Nonprocedural specifies what data is required without specifying how to get those data.
• SQL is the most widely used query language.

SQL

• SQL is a widely used non-procedural language.
• Application programs generally access databases through language extensions to allow embedded SQL
• Application program interface (e.g. ODBC/JDBC) which allow SQL queries to be sent to a database

Database Users

• Users are differentiated by the way they expect to interact with the system.
• Types of users include: application programmers, sophisticated users, specialized users, and naïve users.
• Application Programmers interact with system through DML calls
• Sophisticated users form requests in a database query language
• Specialized users write specialized database applications that do not fit into the traditional data processing framework
• Naive users invoke one of the permanent application programs that have been written previously

Database Administrator

• Coordinates all the activities of the database system.
• Database administrator's duties include schema definition, storage structure, access method definition, and schema and physical organization modification.
• More of a database administrator's duties are to grant user authority to access the database, specifying integrity constraints, act as liaison with users, monitor performance, and respond to requirement changes.

Transaction Management

• A transaction is a collection of operations that performs a single logical function in a database application.
• Transaction-management ensures that the database remains in a consistent (correct) state despite system failures and transaction failures.
• The concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

Storage Management

• The storage manager is a program module that provides the interface between low-level data stored in the database, the application programs, and queries submitted to the system.
• The storage manager is responsible for interaction with the file manager and efficient storing, retrieving, and updating of data.

Overall System Structure

• Shows relationships between users, tools, storage and system admins

Application Architectures

• Two-tier architecture: client programs use ODBC/JDBC to communicate with a database.
• Three-tier architecture: web-based and other applications built using middleware.

Introduction to database systems which includes the purpose and structure of database systems. Includes drawbacks of using file systems to store data, data redundancy and inconsistency, accessing data, data isolation, integrity problems, atomicity of updates, concurrent access by multiple users, and security.