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Characteristics of Data

Characteristics of Data. Data vs. information Data: raw facts Example: printout of tables as they are stored Information: processed data, useful for decision-making Example: formatted report using database. Schema.

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Characteristics of Data

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  1. Characteristics of Data • Data vs. information • Data: raw facts • Example: printout of tables as they are stored • Information: processed data, useful for decision-making • Example: formatted report using database

  2. Schema • A place or repository where the information about the structure of data is stored.

  3. Databaseapplication • A program which is used to retrieve from database

  4. DatabaseManagementSystem (DBMS) • Collection of program that is used to manage the data in the database and users of database.

  5. Advantages of Integrated Databases • Compared with file systems, database can provide • Sharing of data • Control of redundancy • Data consistency • Improved data standards • Better data security • Improved data integrity • Balancing of conflicting requirements • Faster development of new applications • Better data accessibility • Economy of scale • More control of concurrency • Better backup and recovery procedures

  6. Disadvantages of Databases • Compared with file systems, databases have some disadvantages • High cost of DBMS • Higher hardware costs • Higher programming costs • High conversion costs • Slower processing of some applications • Increased vulnerability • More difficult recovery

  7. ConcurrencyControl • Concurrent execution of user programs: key to good DBMS performance. • Disk accesses frequent, pretty slow • Keep the CPU working on several programs concurrently. • Interleaving actions of different programs: trouble! • e.g., account-transfer & print statement at same time • DBMS ensures such problems don’t arise. • Users/programmers can pretend they are using a single-user system. (called “Isolation”) • Thank goodness! Don’t have to program “very, very carefully”.

  8. Is data a resource?

  9. Four Levels of Data • Real world • Enterprise in its environment • Mini-world, or Universe of Discourse – part of the world that is represented in the database • Conceptual Model • Entities, entity sets, attributes, relationships • Logical model of database • Metadata, data about data • Record types, data item types, data aggregates • Stored in data dictionary • Data occurrences • Database itself • Data instances • files

  10. Four Levels of Discussing Data

  11. DatabaseUsers • Application Programmer • End users • Database Administrator

  12. ApplicationProgrammer • Writes application program using tools

  13. EndUsers • Naïve end users • Sophisticated end users

  14. DatabaseAdministrator • A person who has central control over data and programs that access this data • Schema deification • Granting data access • Routine maintenance • Backup • Monitoring disk space • Monitoring job running

  15. Database Administrator Skills • DBA must be • Technically competent • Good manager • Have excellent interpersonal and communication skills • Has primary responsibility for planning, designing, developing and managing the operating database • Database designer may do conceptual and logical design; DBA does physical design, implementation, develops, manages system

  16. Databasedesigner • Responsible for identifying the data to be stored in the database and choose the appropriate structure to represent and store data.

  17. Databaseusers

  18. Workersbehindthescene • DBMS system designer and implementer • Tool developer • Operators and maintenance personnel

  19. DatabaseArchitecture • Separate users view from the physical representation why we need it

  20. Three-level Database Architecture • CODASYL DBTG and ANSI/X3/SPARC reports proposed viewing database architecture at 3 levels of abstraction – external, logical, internal - each with a written description called a schema • Rationale for separation of external and internal levels • Different users need different views of same data • Users data needs may change over time • Hides complexity of database storage structures • Can change logical structure without affecting all users • Can change data and file structures without affecting overall logical structure or users' views • Database structure unaffected by changes to the physical aspects of storage • See Figure 2.5

  21. External Level • Consists of many user models or views • Has external records - records seen by users • May include calculated or virtual data • Described in external schemas (sub-schemas) • Used to create user interface

  22. Logical Level • Entire information structure of database • “community view” as seen by DBA • Collection of logical records • All entities, attributes, relationships represented • Includes all record types, data item types, relationships, constraints, semantic information, security and integrity information • Relatively constant over time • Described in logical schema • Used to create logical record interface

  23. Internal Level • Physical implementation level • Includes data structures, file organizations used by DBMS • Depends on what DBMS is used • Described in internal schema • Used to create stored record interface with operating system • Operating system creates physical files and physical record interface, below DB

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