CPSC-608 Database Systems Fall 2009 Instructor: Jianer Chen Office: HRBB 309B Phone: Notes #2

secondary storage (disks) in tables (relations) database administrator DDL language database programmer DML (query) language DBMS file manager buffer manager main memory buffers index/file manager DML complier DDL complier query execution engine transaction manager concurrency control lock table logging & recovery graduate database

secondary storage (disks) in tables (relations) database administrator DDL language database programmer DML (query) language DBMS file manager buffer manager main memory buffers index/file manager DML complier DDL complier query execution engine transaction manager concurrency control lock table logging & recovery A Quick Review on Undergraduate Database

We have agreed Information (i.e., database) is organized in tables (i.e., relations) stored in disks.

We have agreed Information (i.e., database) is organized in tables (i.e., relations). ● How is information represented by relations? ● What are “good” table structures? ● What operations can we apply on tables?

How is information represented by relations?

Information consists of ● objects (i.e., entities) plus ● connections (i.e., relationships) among entities

How is information represented by relations? Information consists of ● objects (i.e., entities) plus ● connections (i.e., relationships) among entities Thus, information can be given by Entity/relationship (R/E) diagrams

How is information represented by relations? Information consists of ● objects (i.e., entities) plus ● connections (i.e., relationships) among entities Thus, information can be given by Entity/relationship (R/E) diagrams Read: Sections

How to convert E/R diagrams into relations (i.e., tables)?

Fairly straightforward:

How are E/R diagrams converted into relations (i.e., tables)? Fairly straightforward: ● an entity set is given by a table where each column corresponds to a property (i.e., attribute) of the entities; ● a relationship among entities is given by a table whose columns correspond to the identifications of the related entities (that now become attributes).

How are E/R diagrams converted into relations (i.e., tables)? Fairly straightforward: ● an entity set is given by a table where each column corresponds to a property (i.e., attribute) of the entities; ● a relationship among entities is given by a table whose columns correspond to the identifications of the related entities (that now become attributes). Read: sections 4.5.

What are “good” table strcutures? ● have no inconsistency; ● avoid redundancy; ● easy to use

What are “good” table strcutures? ● have no inconsistency; ● avoid redundancy; ● easy to use Typical questions: ● Should we split a table when it is too fat? ● Should we merge tables when they are too thin?

What are “good” table strcutures? ● have no inconsistency; ● avoid redundancy; ● easy to use Typical questions: ● Should we split a table when it is too fat? ● Should we merge tables when they are too thin? Read: Chapter 3.

Some terminology namemanf WinterbrewPete’s Bud LiteAnheuser-Busch Beers Attributes (column headers) Tuples (rows) Relation, attribute, tuples a relation

Some terminology Keys and superkeys Superkey: a set of attributes that uniquely determines a tuple; Key: a superkey that does not contain any smaller superkey.

Some terminology Relation schema: relation name and attribute list. Database schema: set of all relation schemas in the database. Database: collection of relations.

Relational operations Typically, selecting tuples that meet a given condition.

Relational operations Core relational operations: Union, intersection, and difference. –Usual set operations; –Extended to bags Selection: picking certain rows. Projection: picking certain columns. Products and joins: compositions of relations. Renaming of relations and attributes.

Relational operations extended relational operations: ● δ = eliminate duplicates from bags. ● τ = sort tuples. ● γ = grouping and aggregation.

Relational operations extended relational operations: ● δ = eliminate duplicates from bags. ● τ = sort tuples. ● γ = grouping and aggregation. Read: Chapter 5