1. INTRODUCTION TO DBS Database: a collection of data describing the activities of one or more related organizations DBMS: software designed to assist in maintaining and utilizing large collections of data Why not OS file systems? Efficient disk I/O Identifying data items efficiently security query processing concurrency control integrity Levels of abstraction External schema: user views Conceptual (logical) schema: description of data items Physical schema: storage details, access structures Data independence: application programs insulated from data structure and storage Logical data independence physical data independence

2. OTHER DBMS FEATURES Queries: user requests for data definition and manipulation DDL DML host language query language based on relational calculus: based on mathematical logic relational algebra: based on operators Concurrent access and crash recovery transaction: each execution of a user program isolation: each transaction is independent of others atomicity: either all actions or none are carried out durability: effect of transaction should be crash proof locking protocol shared lock exclusive lock transaction log write-ahead log

3. DBMS CONTD. Advantages of a DBMS Data independence Efficient data access Data integrity and security Data administration Concurrency and crash recovery Reduced application development time People who deal with databases Implementers End users DBAs designing a database security and authorization data availability and recovery from failures

4. Client/server and Distributed Databases File servers in LANs DB stored in one or more servers attached to a LAN data storage record locking DBMS stored in each client data integrity data security table scan Application programs are stored in each client Forms (screens) Reports Queries Client sends data requests to server(s) Server sends data files and lock status to client Limitations significant network traffic each client runs a full version of the DBMS data integrity and record locking is managed by clients: impractical

5. Client/server architecture Instead of sending data files, just send the result of a query Client: user interface for presenting data to the user sends queries over the network to the server runs any application programs necessary displays the results of the queries to the user Server: contains DBMS and DB processes queries sends results back to clients Benefits client and server are loosely coupled, may be running on different platforms: open systems reduced network traffic division of processing power between client and server Issues: substantial processing power for server required backup, recovery, security requires specialized tools such as DB servers, APIs standards for data/program distribution strategy, data transfer protocol data partitioning across multiple servers