Chapter 1 Introduction Yonsei University 1 st Semester, 2014 Sanghyun Park

Database Management System (DBMS)  Collection of interrelated data  Set of programs to access the data  DBMS contains information about a particular enterprise  DBMS provides an environment that is both convenient and efficient to use  Databases touch all aspects of our lives

Purpose of Database System  In the early days, database applications were built on top of file systems  Drawbacks of using file systems to store data:  Data redundancy and inconsistency  Difficulty in accessing data  Integrity problems  Atomicity of updates  Concurrent access by multiple users  Security problems  DBMS offers solutions to all the above problems

View of Data  An architecture for a database system

Data Models  A collection of tools for describing  Data  Data relationships  Data semantics  Data constraints  Entity-Relationship model  Relational model  Other models:  Object-oriented model, semi-structured data models  Older models: network model and hierarchical model

Entity-Relationship Data Model

Relational Model

Data Definition Language (DDL)  Language for defining the database structure create table instructor ( IDchar(5), namevarchar(20), dept_namevarchar(20), salarynumeric(8,2) )  Execution of the above DDL statement creates the instructor table  In addition, it updates a special set of tables called the data dictionary

Data Manipulation Language (DML)  Language for accessing and manipulating the data organized by the appropriate data model  Procedural DMLs require a user to specify what data are needed and how to get those data  Declarative (or Nonprocedural) DMLs require a user to specify what data are needed without specifying how to get those data  It is common to use the terms query language and data manipulation language synonymously  SQL is the most widely used query language

Database Access From Applications  Application programs are programs that are used to interact with the database  Application programs are usually written in a host language, such as Cobol, C, C++, or Java  Application programs generally access databases through one of:  Language extensions to allow embedded SQL  Application program interface (e.g., ODBC/JDBC) which allows SQL queries to be sent to a database

Application Architecture  Two-tier architecture: E.g. client programs using ODBC/JDBC to communicate with a database  Three-tier architecture: E.g. web-based applications

Overall Database System Structure

Storage Management  A program module that provides the interface between low-level data stored in the database and application programs and queries submitted to the system  Issues  Storage access  File organization  Indexing and hashing

Query Processing  Parsing and translation  Optimization  Evaluation

History of Database Systems (1/2)  Late 1960s and 1970s  Network and hierarchical data models in widespread use  Ted Codd defines the relational data model (Win the ACM Turing Award for this work) (IBM Research begins System R prototype) (UC Berkeley begins Ingres prototype)  1980s  Research relational prototypes evolve into commercial systems (SQL becomes industrial standard)  Parallel and distributed database systems  Object-oriented database systems

History of Database Systems (2/2)  1990s  Large decision support and data-mining applications  Large multi-terabyte data warehouses  Emergence of Web commerce  2000s  XML and XQuery standards  Automated database administration