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Data Management I DBMS Relational Systems Overview Introduction DBMS – components – types Relational Model – characteristics – implementation Physical Structure File-based Systems Collection of applications that performs services for end user- programs define and manage data Limitations – Data dependence-structure defined in program – Incompatible file formats – Programs written to satisfy function Database Definition A database system is essentially a computerized record keeping system whose overall purpose is to maintain information and make it available on demand Advantages of Database REDUCED REDUNDANCY - Controlling duplication INTEGRATION AND SHARING OF DATA - One set of data to maintain MAINTAINING CONSISTENCY - Data propagation DATA ACCESS - Multiple access paths; High level language STANDARDIZATION - Enforcing local and global standards SECURITY - User access; Protection of Data DATA INDEPENDENCE - Data descriptors separate from application program Increased integrity and concurrency control Components of a Database System Data – Note: Date uses data and information interchangably Hardware – Processor, main memory, secondary storage and I/O devices – Individual PC to a network of computers Software – DBMS – Application programs – Others software tools Users – Application Programmers – End - Users – DBA’s Procedures ?? Database Management System DBMS Software Software Components – Data Definition DDL source form object form – Data manipulation DML planned request unplanned request – Data administration DAL Data security and recovery – Integrity and concurrency – Performance – Data dictionary Data Dictionary Catalog Repository Database of information about a database – description of all database objects – references to all users of the database – references to all programs and transactions that access the database Provides the description of the data to enable program-data independence Database Models Hierarchical - IMS – tree structure with predefined access paths – child has one parent Network - CODASYL - IDMS – multiple paths to same record Multi-dimensional Object-oriented – data and methods – highly-variable structure – tightly coupled with programming language Hybrid - Object/Relational Databases Relational Model Evolving System - System designed by Codd, partially implemented, developing Theoretical Vs Available - No system met Codd’s original 12 rules. Degrees of relational defined Date’s work - Supportive of relational model but not always in agreement with Codd Functions of a DBMS Data – Must furnish users with the ability to store, retrieve, and update data in the database. A User-Accessible Catalog. – Storage, Retrieval and Update. Must furnish a catalog in which descriptions of data items are stored and which is accessible to users. Transaction Support – Must furnish a mechanism to ensure that either all the updates corresponding to a given transaction are made or that none of them are made. Functions of a DBMS Concurrency Control Services – Must furnish a mechanism to ensure that database is updated correctly when multiple users are updating the database concurrently. Recovery Services – Must furnish a mechanism for recovering the database in the event that the database is damaged in any way. Authorization – Services Must furnish a mechanism to ensure that only authorized users can access the database. Functions of a DBMS Support for Data Communication – Integrity Services – Must furnish a means to ensure that both the data in the database and changes to the data follow certain rules. Services to Promote Data Independence – Must be capable of integrating with communication software. Must include facilities to support the independence of programs from the actual structure of the database. Utility Services – Should provide a set of utility services. ANSI/SPARC Architecture EXTERNAL LEVEL (individual user view) CONCEPTUAL LEVEL (community user view) INTERNAL LEVEL (storage view) ... External Level Users’ view of the database Language – Application programmer – End-user External View – Logical record – Data authorized to view External Schema Conceptual Level Community view of database Representation of entire information content Conceptual schema – definition of total database content ++ – data independent Internal Level Low-level representation of entire database – occurrences Describes how the data is stored in the database Not physical level Level used by utilities to increase performance. Differences between Three Levels of ANSI-SPARC Architecture 11 Data Independence and the ANSI-SPARC Three-level Architecture Data Model Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. Data Model comprises: – A structural part – A manipulative part – Possibly a set of integrity rules Data Models Object-based Data – Entity-Relationship – Semantic – Functional – Object-Oriented Models Record-based Data Models – Relational Data Model – Network Data Model – Hierarchical Data Model Physical Data Models Client/Server Client/server architecture Front end Back end Middleware model naturally fits the Client/Server Front End GUI Applications Fat vs thin client Should any data be stored in front end? Back End Server Data Shared DBMS Database information Fat server vs thin server Should server contain applications? Middleware Enables front end to speak to back end. Middleware can be as simple as API’s and as complex as Tuxedo software Determinants – variety of databases – networks – size Summary of Client-server Functions