CS 430 Database Theory

CS 430Database Theory Winter 2005 Lecture 2: General Concepts

Example of a Database • Picture of a Database • See Figure 1.2 of Text Book • Two Views of the Data • See Figure 1.4 of Text Book

Data ModelsA Model for Describing Data • Examples: • Relational • Legacy: Network, Hierarchical • Object, Object-Relational • Entity/Relationship (ER) • Typically used for “data modeling” • Typically includes: • Definition: What kind of structures can be defined • Basic Data Manipulation • Except for ER Model

Relational Data Model • Data is organized into Tables • Rows = Records • Columns = Fields • Tables are related by data values • Data related by shared data values • Data manipulation: • Insert a record • Update and delete records • Select records a collection of fields from one or more records

Network and Hierarchical Models • Data organized into Programming Language records • Programming language = COBOL! • Records organized into Sets • Each set has an owner • Hierarchical: Record is member of one set • Methods provided to link records • Network: Record can be member of multiple sets • Data Manipulation: • Traverse sets • Insert, Modify, Delete records • Change set memberships

Object and Object/RelationalData Models • Object: • C++ (typical) style objects stored in database • Manipulated by manipulating records in memory • Objects can have methods as well as data • Object/Relational • Relational at core • Rows treated as objects • Supports object concepts such as inheritance, methods, etc.

Entity/Relationship (ER) • Used for data modeling • Data organized into Entities which have attributes • Entities are connected via named relationships • Tools available which can convert from ER model to Relational Schema

Data Modeling • Data modeling builds data models • Yes, we have duplicated terminology • Data modeling: • Develop a model for the data that will be stored and manipulated by a database applications

Categories of Data Models • Conceptual or High-Level • Model the data as seen by the user • Typically incomplete • Answers question: Do we have all the data requirements? • Logical or Representational • Model the data as seen by the application developer • Should have all the Entities, Attributes and Relationships (ER) or Tables, Columns, DataTypes (Relational) identified • Physical or Low-Level • The data as seen by the database administrator • All the physical information available • Where data is stored, indices, etc.

Schema, States • The database schema is the description of the database • The schema is the Intension of the database • As the database is modified it moves from state to state • The DBMS is responsible for guaranteeing that each state is consistent (in accord with the schema) • A database state is the Extension of the schema

Three Schema Architecture • See figure 2.2 in Text Book • Internal Schema • The actual schema of the database • Conceptual Schema • How the data is organized • External Schemas • Individual user and/or application views of the data

Three Schema Architectureand Data Independence • Logical Data Independence • Can change Conceptual Schema without changing External Schemas • Always true to some extent: • Add new Records or Tables • Add new columns? new Relationships? • Change representation of data items (e.g. numbers)? • Physical Data Independence • Can change internal Schema without changing Conceptual Schema • Also always true to some extent • Where records are stored on disk • Add new access paths?

Data Languages • Data Definition Language (DDL) • Define the schema, create the catalog • Data Manipulation Language (DML) • Query the database and change the state of the database • Can be non-procedural (SQL) or procedural (OO) • View Definition Language (VDL) • Define external views • Storage Definition Language (SDL) • How data is stored on disk

Data Languages (continued) • An ordinary programming language (e.g. C, Java) is a host language • DML embedded in a host language is a data sublanguage • May require a preprocessor • May be an Application Programming Interface (API) • Queries, e.g. may be Character Strings • DML outside of a host language is a “Query Language” • Even if it can update the database

Three Schema ArchitectureBottom Line • Nice idea • Reality: • The three levels are not cleanly separated • Applications (external) are reasonably well insulated from internal changes • Except, of course, for performance • Example:SQL • There is no separate VDL, this is part of DDL • DDL can include physical information,e.g. indices • Conceptual schema is simply table definitions with the physical portion removed

Database Components • See Figure 2.3, Text Book • Applications can use either precompiled interface or “ad hoc” interface • Ad hoc interface is the same one used by Interactive Query tools • Stored Data Manager can include Buffer Management • Or this may be left to Operating System

Database Utilities • “Bulk loading” of data into the database • Convert from an external text format for data to the DBMS internal format • Integrated with the DBMS for efficiency • Backup and Restore • May include incremental backup • Knows DBMS structure, so can save consistent picture of the database • Reorganization • Schema changes and/or performance improvement • Performance monitoring • Help to improve database performance

Application Development • Data Dictionary • Description of all the data • All the ancillary information, e.g. units of measure • Host language API • For almost any host language • ODBC (Open Database Connectivity) • Host language precompilers • Convert embedded DML (typically) into host language API • Application Development Environments • Can be extremely sophisticated

Two-tier Three-tier Two-Tier and Three-Tier Database Applications Client Client Application and/or Web Server Database Database

Classification of DBMS • Data Model • Single or Multi-User • Multi-User typical • General or special purpose • Centralized or Distributed • Distributed: Homogeneous or Federated • Transaction processing (OLTP) versus Decision Support (OLAP)

CS 430 Database Theory