1 / 25

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.

zocha
Télécharger la présentation

Characteristics of Data

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related