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Database Files: Physical and Logical Files

Learn about physical and logical files in a database, including their creation, attributes, and uses. Understand how to enter and view data, as well as sort and select data using logical files.

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Database Files: Physical and Logical Files

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  1. IBC233 Week 5

  2. Important Dates • 2nd part of Lab 4 (Lab 4 CL) is due Oct 14/15 • Demonstration • Lab 7 due in lab period after break week • Test 1 – Oct 13/14

  3. Agenda • Database Files • Physical files • Logical files

  4. Database Files

  5. DB2 Database Files • Physical Files *FILE PF-DTA • Logical Files *FILE LF

  6. Physical Files • It is an system i file used to store data or source code. • Physical files have members. • The members contain data or source code. • Source physical files have many members eg. One for each program • Data physical files usually have 1 member (but can have more)

  7. How do we create data physical files?

  8. Creating Physical Data Files • Creating an iSeries data file is very similar to creating a program: • Write the source code (the source code will describe what the file will look like). The source code is stored in a member in a source file. • Compile the source code (this creates a *file object).

  9. Tools for Describing Database Files • Data Description Specifications (DDS) • system i language to create source code for Files • SQL (Structured Query Language

  10. Layout of a DDS Program • File level keywords • Eg. UNIQUE, Function Keys • Record format name • Shouldn’t be the same name as the object • List the fields • Name, type, size and functions • TEXT (used by DFU and DSPFFD) • COLHDG (used by Query/400) • Access Path information

  11. Item File • Write the DDS code to define a *FILE that has the following attributes: • Item Number (5 numeric – 1 digit/byte) • Also the primary key • Item Name (30 Alphanumeric) • Stocking Size (5 Alphanumeric) • In Stock Quantity (7 numeric including 2 decimals – 2 digit/byte) • Date Last Updated

  12. Unique feature of system i Files • The record description is stored with the file object (externally described file) • It can then be used by system i utilities • The record description does not have to be coded in programs that use it. • Can be viewed using DSPFD, DSPFFD

  13. Entering data • If the compile was successful, you will have a new object in your library, a physical file. • To enter data into that file, use DFU, Data File Utility • UPDDTA

  14. DFU • STRDFU, then option 5 or… • PDM option 18 • F10 to enter new records (entry mode) • F11 to change records (change mode), page up and down to find records • F23 to delete a record

  15. Viewing records • RUNQRY QRYFILE(filename) • DSPPFM filename

  16. Access Paths Allows us to sort or select/omit data

  17. Logical Files

  18. Logical Files • Resort data in a physical file • Select/Omit specific sets of data • Hide data • Join or Merge physical files together

  19. Why a logical file • A customer file is made up of customer records (1 per customer). Each customer record has fields containing unique pieces of info about a particular customere.g. customer name, address, sales territory,billing info, shipping instructions,credit information • If we want to make sure that the customer id is unique • If we want to display customer records sorted by name • If we want to select customers in a specific territory • If we want to provide a maintenance screen hiding Credit Information

  20. Creating a Logical File • Create the source file (CRTSRCPF) which is named QDDSSRC (only done once) • Create a source member, type LF • Enter the source code using SEU • Save source code and compile to create the file • Put data into the file.

  21. Create a logical file that sorts Item file by Name and Stocking Size

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