Introduction to Database Systems Ref. Ramakrishnan & Gehrke Chapter 1 The slides for this text are organized into chapters. This lecture covers Chapter 1. Chapter 1: Introduction to Database Systems Chapter 2: The Entity-Relationship Model Chapter 3: The Relational Model Chapter 4 (Part A): Relational Algebra Chapter 4 (Part B): Relational Calculus Chapter 5: SQL: Queries, Programming, Triggers Chapter 6: Query-by-Example (QBE) Chapter 7: Storing Data: Disks and Files Chapter 8: File Organizations and Indexing Chapter 9: Tree-Structured Indexing Chapter 10: Hash-Based Indexing Chapter 11: External Sorting Chapter 12 (Part A): Evaluation of Relational Operators Chapter 12 (Part B): Evaluation of Relational Operators: Other Techniques Chapter 13: Introduction to Query Optimization Chapter 14: A Typical Relational Optimizer Chapter 15: Schema Refinement and Normal Forms Chapter 16 (Part A): Physical Database Design Chapter 16 (Part B): Database Tuning Chapter 17: Security Chapter 18: Transaction Management Overview Chapter 19: Concurrency Control Chapter 20: Crash Recovery Chapter 21: Parallel and Distributed Databases Chapter 22: Internet Databases Chapter 23: Decision Support Chapter 24: Data Mining Chapter 25: Object-Database Systems Chapter 26: Spatial Data Management Chapter 27: Deductive Databases Chapter 28: Additional Topics

What Is a DBMS? A very large, integrated collection of data. Models real-world enterprise. Entities (e.g., students, courses) Relationships (e.g., Tarkan is taking CENG351) A Database Management System (DBMS) is a software package designed to store and manage databases.

Why Study Databases?? ? Shift from computation to information at the “low end”: scramble to webspace (a mess!) at the “high end”: scientific applications Datasets increasing in diversity and volume. Digital libraries, interactive video, Human Genome project, EOS project ... need for DBMS exploding DBMS encompasses most of CS OS, languages, theory, “AI”, multimedia, logic

Why Use a DBMS? Data independence and efficient access. Reduced application development time. Data integrity and security. Uniform data administration. Concurrent access, recovery from crashes. 3

Data Models A data model is a collection of concepts for describing data. A schema is a description of a particular collection of data, using the given data model. The relational model of data is the most widely used model today. Main concept: relation, basically a table with rows and columns. Every relation has a schema, which describes the columns, or fields. 5

Example: University Database Conceptual schema: Students(sid: string, name: string, login: string, age: integer, gpa:real) Courses(cid: string, cname:string, credits:integer) Enrolled(sid:string, cid:string, grade:string) Physical schema: Relations stored as unordered files. Index on first column of Students. External Schema (View): Course_info(cid:string,enrollment:integer) 7

Instance of Students Relation Students( sid: string, name: string, login: string, age: integer, gpa: real ) sid name login age gpa 53666 Jones jones@cs 18 3.4 53688 Smith smith@ee 18 3.2 53650 Smith smith@math 19 3.8

Levels of Abstraction Many external schemata, single conceptual(logical) schema and physical schema. External schemata describe how users see the data. Conceptual schema defines logical structure Physical schema describes the files and indexes used. External Schema 1 External Schema 2 External Schema 3 Conceptual Schema Physical Schema Schemas are defined using DDL; data is modified/queried using DML. 6

Data Independence Applications insulated from how data is structured and stored. Logical data independence: Protection from changes in logical structure of data. Physical data independence: Protection from changes in physical structure of data. One of the most important benefits of using a DBMS!

Files and Access Methods These layers must consider concurrency control and recovery Structure of a DBMS A typical DBMS has a layered architecture. This is one of several possible architectures; each system has its own variations. Query Optimization and Execution Relational Operators Files and Access Methods Buffer Management Disk Space Management DB 22