MSc IT UFIE8K-10-M Data Management Prakash Chatterjee Room 3P Lecture 9 : DBMS Architecture

UFIE8K-15-M Data Management ANSI/SPARC Architecture Problem of Data independence In ‘classical systems’ Application programs ‘know’ about how and where data is stored Problems when additional data stored but not of relevance to prog data reorganised for efficiency but no change in content

UFIE8K-15-M Data Management ANSI/SPARC (2) Two distinctions between the global ‘logical’ data model and the way the data is stored in physical data storage on disk isolates issues of efficient storage such as indexes, replication of data for fast access and backup between local application programs and the global data model isolates functional areas from concern for the full conceptual model - remember ISIS has 250 tables

UFIE8K-15-M Data Management ANSI/SPARC (3) External view - defines VIEWS which bring together a subset of the full model for a specific functional area - e.g. enrolment Conceptual model - full ‘logical’ model of the organisation Physical - storage of data in underlying files using the appropriate file structures, and allocated to storage units

UFIE8K-15-M Data Management ANSI/SPARC example Lecturer view of ISIS those students which she teaches (restriction) relevant data items (projection) denormalised (eg. name and award name by module) Full model is 250 tables Physical data storage duplicates key files for fast retrieval builds indexes based on common queries

UFIE8K-15-M Data Management DBMS Software Components User programs user developed programs (eg. as VB Macros, PLSQL procedures, PHP scripts,stored Queries) DBMS Toolkit tools to help user build systems and user programs Interface language and protocol for communication between User programs and Kernel Kernel core Database functions - data storage and retrieval Operating System - file storage

UFIE8K-15-M Data Management Interface User programs need to communicate with the Kernel to update the Schema (Data Definition Language) update the Factbase (Data Manipulation Language) Interface must handle: sending requests to the Kernel e.g. with SQL receiving results from the Kernel linking to Kernel, handling errors (e.g ODBC,JDBC) Receiving results is tricky: send whole relation in some serialized format send pointer to temporary table and get each row

UFIE8K-15-M Data Management Interface (2) Scripting languages such as PL/SQL (Oracle’s application language) and PHP (a Web server language) send SQL and provide routines for access to the results e.g. the notion of a ‘CURSOR’ a pointer to the next row of a table to be returned Access can automate this connection so that a table located on a remote server ‘appears’ to be a local table.

UFIE8K-15-M Data Management Kernel functions CRUD - Create, Read, Update, Destroy at Factbase and Schema level Data Dictionary - Schema storage Transaction Management - run-unit completion Concurrency Control - multiple users Recovery - backup and restore Authorisation - users, passwords, areas Data Communications ( or by OS) Data integrity - foreign keys etc. Import/Export, Monitoring

UFIE8K-15-M Data Management Kernel (2) Schema table definitions integrity constraints views (stored queries) access control Stored in Data Dictionary DD is a Database itself, the System Catalog Manipulated with DDL and DCL Factbase tables Manipulated with DML Interface with operating system for file access Transaction control concurrency locking

UFIE8K-15-M Data Management Toolkit - Application Development Tools e.g. Access Graphical User Interface (GUI) QBE to generate SQL queries Form and report definitions VB Macros for user programs Natural Language Interface translation from natural language to SQL

UFIE8K-15-M Data Management User programs SQL command line interface SQLPlus for Oracle, similar for MySQL Pre-compiler (COBOL..) Program contains SQL statements which need to be compiled into calls to Kernel functions Scripts (PHP,Perl) Generation of SQL calls at runtime

UFIE8K-15-M Data Management CASE tools Select SSADM, Rational Rose, Oracle Designer 2000 allow developers to develop schema from ER model

UFIE8K-15-M Data Management Admin tools Database software control starting and stopping Kernel backup and restore Reconstruct indexes Access control create users, user groups, assign user access rights to tables Import and Export of data and schema Schema migration - major schema change monitoring and tuning

UFIE8K-15-M Data Management Kernel operations Underlying file types Indexing Transactions Locks Rollback Query optimisation

UFIE8K-15-M Data Management Physical organisation Secondary storage (on disk) divided into blocks - say 16K in size For a given file system, blocks have control info(index to records in block..) and free space as well as user records structured blocks are called ‘pages’ Data is transferred between main memory and secondary storage in pages Pages can be held in memory (cached) for speed of access