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