Database Organization and Design Chapter 1 Adapted from slides by Raghu Ramakrishnan, raghu@cs.wisc.edu

What is a DBMS? A database is a (very) large, integrated collection of data A database is based upon a data representation (data model) of a real-world enterprise Objects (or Entities, e.g., students, courses) Relationships (e.g., Charlie Brown is in CS3610) A Database Management System (DBMS) is a software package designed to store and manage databases. E.g., UNIDATA, mysql, or Access

File Storage vs. a DBMS A DBMS can “stage” data (for large datasets) between main memory and secondary sources (disk, CD, tape) A DBMS provides efficient (indexed) access A DBMS provides a built-in query language to facilitate data retrieval Permits free form queries Standard language provides standard communication for programs using embedded queries A DBMS protects data from inconsistency by Enforcing referential integrity during data modification Enforcing data format constraints Providing controlled concurrent access A DBMS provides crash recovery A DBMS provide multi-level security and access control A DBMS allows for uniform administration of the data

Data Models A data model is the manner in which you describe some data. The Entity Relationship Diagram (ERD) represents a conceptual data model for describing objects and their relationships. The ERD is the most common of the conceptual data models. It has several variants. Main features of an ERD is entities, attributes, and relationships. The relational data model is a conceptual data model for implementing a database. The relational model is easily the most widely used model today. Main concept the relation: a table of records and fields Every relation has a defining schema A schema is the description of a particular collection of data in a given data model.

Levels of Abstraction View 1 View 2 View 3 Conceptual Schema Physical Schema

Example: University Database External View: View1: course_info ( course_name, enrollment ) View2: teacher_info ( course_name, teacher ) Conceptual Schema Students(sid, name, age, gpa) Courses (cid, name, credits) Teachers (tid, name, rank) Enrolled (sid, cid, grade) Teaches (tid, cid) Physical Schema Store relations as tables Index tables by id fields

Road Ahead Modeling Data with Entity Relationship Diagrams Using the Relational Model (i.e., Schema Descriptions) to Model Data Relational Algebra: A concise language for describing data operations Structured Query Language (SQL): A standard language for manipulation of data by computers Database Apps: Learning how to access databases from programs Database File Organization, Storage, and Indexing

Road Ahead (Continued) Hash Indexes Query Evaluation: Getting the resultant data for the (somewhat) least cost Transaction Management: Keeping multiple users from interfering with each other Schema Design and Normal Forms: Reducing redundancy in the database Physical Database Design: Tuning your database for performance