Intro – Part 2 Introduction to Database Management: Ch 1 & 2

Important Points DBMS Functions DBMS Architectures Database Development Phases

Functions of a DBMS Eight services that a DBMS should provide (Codd82): 1) Data storage, retrieval, and update 2) A user-accessible catalog describing data items 3) Transaction support 4) Concurrency control services 5) Recovery services 6) Authorization (security) services 7) Support for data communication (network access) 8) Data integrity services

Database System Approach

Components of a DBMS A DBMS is a complicated software system containing many components:  Query processor - translates user/application queries into low-level data manipulation actions. Sub-components: query parser, query optimizer  Storage manager - maintains storage information including memory allocation, buffer management, and file storage. Sub-components: buffer manager, file manager  Transaction manager - performs scheduling of operations and implements concurrency control algorithms.  Access manager – controls access to a database

Overall System Structure

Database Architectures There are several different database architectures: File-server architecture - files are shared but DBMS processing occurs at the clients (e.g. Microsoft Access) Two-Tier client-server architecture - dedicated machine running DBMS accessed by clients (e.g. SQL Server, MySQL) Three-Tier client-server architecture - DBMS is bottom tier, second tier is an application server containing business logic, top tier is clients (e.g. Web browser/Web Server/PHP/MySQL)

Two-Tier Client-Server Architecture Advantages: Only one copy of DBMS software on dedicated machine. Increased performance. Reduced hardware and communication costs. Easier to maintain consistency and manage concurrency.

Three-Tier Client-Server Architecture Advantages: Reduced client administration and cost using thin web clients. Easy to scale architecture and perform load balancing.

Database Development Phases Conceptual Data Modeling Logical Database Design Distributed Database Design Physical Database Design ERD Tables Distribution Schema Internal Schema, Populated DB Data requirements

Conceptual Data Modeling Information content of the database Entity relationship diagram (ERD) showing entity types and relationships Diverse formats for database requirements

Logical Database Design Refine conceptual design Convert ERD to table design Normalization: tool to reason about redundancies Add constraints to enforce business rules

Physical Database Design Performed at each independent database site Minimize response time without consuming excessive resources Tradeoffs: retrieval versus update Flexible designs versus specialized designs Decisions: indexes, data placement