5. Client-Server Databases and Tools

Transcription

1 5. Client-Server Databases and Tools

2 Client-Server Database (SQL Server) A multiuser relational database management system Transaction oriented processing Security through accounts, permissions and views Rules and triggers to enforce integrity Examples: Oracle, SQLServer, DB2, Informix, Sybase 75

3 Criteria for Selecting SQL Servers Cost Openness Vendor support and position Third party support Scalability Extra features 76

4 How Front-end Tools Work User creates query Front-end formats query and sends it to the DBMS Client System Database server checks user s security rights Database server processes the query and returns the results to the front-end Server System Front-end receives the response and formats it for the user User view and/or manipulate the data Client System 77

5 Front-end Tools Categories Adds on to existing products Require more system resources Application development tools OLTP (on-line transaction processing) Programming Query/reporting tools Nonprogramming Data integration and analysis tools EIS/DS (executive information/decision support) 78

6 Few Leading Tools Application development tools Developer 2000 Oracle PowerBuilder Powersoft Visual Basic Microsoft Access Microsoft Data integration and analysis tools Forest & Trees Query/reporting tools 79

7 Evaluating Front-end Tools Easy coding Scripting language 4GLs Object-oriented features Call 3GL modules Multiprogrammers features Local prototyping opportunity Off-line development Rapid application development 80

8 ... Evaluating Front-end Tools Broad back-end support Adherence to existing standards ODBC Accessibility of server-specific features Cross-platform development Openness Integration with existing tools Features, not price 81

9 Database Languages Integrated with a programming language dbase Language, Access High-Level Database Languages SQL Declarative Set-at-a-time Interactive Embedded in a host language User-friendly Query Languages QBE 4GL tools 82

10 SQL Structured Query Language Originally was called SEQUEL The standard language for relational DBMS Developed by IBM in 1972 SQL = DDL + DML + DCL 83

11 SQL Standards Need for standardization ANSI/ISO SQL standard ANSI 1986 Level 1 Level 2 ANSI X ANSI Integrity Enhancement SQL2 (ANSI 1992) SQL3 (ANSI 1994) 84

12 Stored and System Procedures create procedure procname [paramertes] as sql_statment execute procname 85

13 Triggers A special kind of stored procedure that goes into effect when you modify data in a specified table Triggers are used to maintain integrity create trigger trigname on tablename for {insert, update, delete} as sql_statements drop trigger trigname 86

14 Control-of-Flow Language Batches go IF... ELSE IF Boolean_expression sql_statement ELSE sql_statement BEGIN... END BEGIN statement_block END WHILE Boolean_expression sql_statement 87

15 Methods of Accessing a Database Ad-hoc access Interactive SQL 4GL tools Programmatic access Embedded SQL Call Level Interface (CLI) 88

16 The challenge of Accessing Heterogeneous Databases Data resides on different DBMS Hardware platforms Operating systems Network systems We do not have to wait for fully distributed databases, client-server architecture can address the heterogeneous database access problem Front-end tools can access diverse databases Essential to enterprises with heterogeneous databases 89

17 Embedded SQL Host language Host variables Singleton SELECT Cursors SQL Communication Area (SQLCA) Precompiler Static SQL Dynamic SQL EXECUTE IMMEDIATE PREPARE, EXECUTE 90

18 Call Level Interface A program communicates with the DBMS through a set of function calls called the application program interface (API) The CLI approach is used in client-server architecture The code of the API is located on the client system The SQL API becomes just another library for the programmer to learn No need for a precompiler 91

19 Heterogeneous Database Access Issues Programming interface Embedded SQL or CLI Interprocess communication mechanism Named pipes, TCP/IP Network protocol TCP/IP, NetBEUI, SPX/IPX System catalog SQL syntax and semantics 92

20 Heterogeneous Database Access Approaches Embedded SQL CLI The application should be precompiled with each back-end server it accesses Source Code Compatibility The source code must be recompiled for a new environment Unacceptable solution to software vendors and corporates The ability to connect to various backends on a dynamic basis, by loading a new library Binary Compatibility Dynamic link libraries or database drivers 93

21 Open Database Connectivity (ODBC) Architecture for database connectivity Open Vendor-neutral ODBC interface defines the following ODBC API (function calls) SQL syntax based on X/Open and SQL CAE specs Standard set of error codes Standard way to connect to a DBMS Standard representation for data types 94

22 ODBC Goals Provide universal database access Ease development burden Broadens application support for databases Built-in scalability for applications With ODBC the client application is not required to know Location of the DBMS Communication method What vendor s DBMS is being used 95

23 ODBC Architecture Application Driver Manager ODBC Interface Driver Driver Driver Data Source Data Source Data Source 96

24 Basic Application Steps CONNECT (db, user, pswd) SEND ( select * from... ) EXECUTE ( ) Client Application GETROW ( ) (101, Dhahran,...) GETROW ( ) DBMS (101, Khobar,...) DISCONNECT () 97

25 ... Basic Application Steps Setting up a data source SQLConnect, SQLDriverConnect Sending SQL to the data source SQLPrepare, SQLExecute, SQLExecuteDirect ODBC syntax Pass through Retrieving results SQLFetch Cursors SQLSetScrollOption, SQLSetPos Static, dynamic, Key-set driven 98