1. 1 CS 430 Database Theory Winter 2005 Lecture 2: General Concepts

2. 2 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

3. 3 Data Models A 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

4. 4 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

5. 5 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

6. 6 Object and Object/Relational Data 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.

7. 7 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

8. 8 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

9. 9 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.

10. 10 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

11. 11 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

12. 12 Three Schema Architecture and 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?

13. 13 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

14. 14 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

15. 15 Three Schema Architecture Bottom 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

16. 16 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

17. 17 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

18. 18 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

19. 19 Two-Tier and Three-Tier Database Applications Two-tier Three-tier Client Application and/or Web Server Database Client Database

20. 20 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)