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DATABASE ENVIRONMENT Dream World Case Study • Real World entities Staff, property, Owner and Renters • Attributes describing properties or qualities of each entity • Relationships between these entities (Staff MANAGES Property) ANSI-SPARC three-level architecture View 1 View 2 Conceptual schema Internal schema Database American National Standard Institute (ANSI)Standards Planning and Requirements Committee (SPARC) View n External Level Conceptual Level Internal Level • EXTERNAL LEVEL – User’s view of the database – Part of the database that is relevant to a user • CONCEPTUAL LEVEL – Community view of the database – What data is stored in the database – Relationships among the data – Entities, their attributes and relationships – Security and integrity information INTERNAL LEVEL Physical representation of the database on the computer • Internal level – – – – Storage space allocation of data and indexes Record description for storage Record placement (pointers) Data compression and encryption techniques Differences between the three levels External View 1 External View 2 Sno Staff_No Fname Lname Age Salary Conceptual level Staff_No Lname Branch_No Staff_No Fname Lname DOB Salary Branch_No Struct STAFF { int Staff_No; int Branch_No; Internal level char Fname[15]; char Lname[15]; struct date Date_of_Birth; float salary; struct STAFF *next; //pointer to next staff record }; index Staff_No; index Branch_No; // define indexes for staff DATA INDEPENDENCE • Logical Data Independence: Possibility for addition/removal of new entities, attributes or relationships • Physical Data Independence: Possibility for changes to storage structures Data Independence External schema External/ conceptual mapping External schema External schema Logical data independence Conceptual schema Conceptual/ Internal mapping Physical data independence Internal schema Database Languages • Data definition Language (DDL): – A descriptive language – Name the entities and relationships • Data Manipulation Language (DML): – Data Manipulation Operations: – – – – Insertion of new data Modification of data Retrieval of data Deletion of data DMLTypes • Procedural DML: – What data is needed – How to retrieve this? (record by record) • Non-Procedural DML: – What data is needed rather than how to retrieve it. (based on set of records) 4GL • Query languages, Form generators, Report generators. • Specialty languages such as spreadsheets and database languages • Application generators (define, insert, update and retrieve data) • Program Generators • Graphics generators Data Model • An integrated collection of concepts – For describing data – Relationships – Constraints • Object Based Data Models – Entity – Attributes – Behavior • Record Based Data Model – Relational, Network, Hierarchical, Multidimensional Network Data Model Relational Data Model Multidimensional Data Model Object Oriented Data Model Functions of a DBMS • 1) Data storage, retrieval and update • 2) A user accessible catalog – System Catalog stores : • • • • • • Names, sizes and types of data items Names of relationships Integrity constraints Names of authorized users who have access External, conceptual and internal schemas Usage statistics (Functions contd…) • 2) A user accessible catalog (contd.) – Benefits of a System catalog: • • • • Collection and storage at one place Meaning of the data can be referred Communication is simplified Redundancy and inconsistencies can be identified more easily • Changes to the database can be recorded • Security • Integrity • 3) Transaction Support • 4) Concurrency control services The Lost Update Problem Time T1 t1 T2 balx read (balx) 100 t2 real (balx) balx = balx +100 100 t3 balx=balx-10 write (balx ) 200 t4 write (balx ) t5 90 90 • • • • • • (Functions contd…) 5) Recovery services 6) Authorization services 7) Support for data communication 8) Integrity services 9) Service to promote data independence. 10) Utility services Components of a DBMS Programmers Application Programs DBMS Users Queries DBA Database schema DML Preprocessor Query Processor DDL Compiler Program object code Database Manager Dictionary Manager Access methods System buffers File Manager Database and system catalog Components of a database manager Program Object Code Database manager Integrity Checker Data manager Access Methods System buffers Query processor Catalog Manager Authorization Control Command processor Query Optimizer Transaction Manager Scheduler Buffer Manager Recovery Manager File Manager Databases and system catalogs Teleprocessing Topology File Server architecture Workstation 2 Workstation 1 Workstation 3 A Large amount of network traffic A full copy of DBMS is required on each workstation LAN Concurrency, recovery and integrity control are more complex Request for data database File Server Client Server architecture Client 2 Client 1 Client 3 LAN Request for data Server (with DBMS) Selected data returned database Alternate client-server topologies client Server Single Client Single Server Server Multiple Client - Single Server Client 1 Client 2 Client 1 Multiple Client Server 1 Multiple Server Client 2 Client 3 Server 2 Summary of Client server applications Client • Manages the user interface • Accepts and check syntax of user input • Process application • Generates database requests and transmits to the server • Passes response back to user Server • Accepts and processes database requests from clients • Checks authorization • Ensures integrity constraints not violated • Performs query/ update processing and transmits response to client • Maintains system catalog • provides concurrent database access • Provides recovery control