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Week 1 January 25

Week 1 January 25. Introduction to 4GLs 4GLs versus 3GLs File-based systems versus database. PowerBuilder 4GL Model. Interface. Interface. User. Process. Data. Program. Interface. Conventional File-Based Applications. Records. Text. File-based. Procedural Code. Terminals.

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Week 1 January 25

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  1. Week 1January 25 Introduction to 4GLs 4GLs versus 3GLs File-based systems versus database

  2. PowerBuilder 4GL Model Interface Interface User Process Data Program

  3. Interface Conventional File-Based Applications Records Text File-based Procedural Code Terminals Interface User Process Data Text Procedural Records • 80 x 24 Screen • Characters • Function keys • 3GL program • Files • Hierarchical database

  4. Text-Based Interactive Application Press function key corresponding to a menu option Enter letters corresponding to a menu options Function keys

  5. File-Based System PO Program Invoice Customer Order File One file, one program, one output Account Report Customer Accounts Program Customer Account File Customer Mailings Program Customer Mailing List File Mailing List

  6. File-Based Systems • Records contain logically related data • Limitations: • Separation and isolation of data • Duplication of data • Loss of data integrity • Data dependence • Incompatibility of files • Fixed queries/proliferation of application programs

  7. Data Redundancy • Customer Order File • PO number • Customer account number • Customer name, address, city, state, zip code • Order date • Product code, product description, price, unit • Customer Account File • Account Number • Customer name, mailing address, city, state, zip code • Customer Mailing List File • Customer name, mailing address, city, state, zip code

  8. Interface 4GL Applications GUI Sets Work- stations SQL Interface Database User Process Data GUI Event Driven Set • Windows • Objects • Pictures and graphics • Point and click • Code • RDBMS

  9. Interface Oracle Developer Applications Data GUI Sets Interface Query User Process Data

  10. Interface Interface Oracle Developer Applications Presentation Data Source GUI Sets File Account #: User Process Data • Reports • Forms • Graphs • Triggers (PL/SQL) • Query

  11. Database • “A shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.”

  12. Database Management Queries Customer Orders Application Programs DBMS Order Items Products Manufacturers • DDL • DML • Controlled access Other Software Central Repository Single Access Multitude of Applications

  13. Data Abstraction • Separation between the data’s structure (definition) and the application programs In a procedural language program such as COBOL... FD Master-File. 01 Master-Record. 05 ID PIC X(10). 05 Customer-Fname PIC X(25). . . . Tightly binds the data file and program

  14. Data Abstraction • Separation between the data’s structure (definition) and the application programs In a procedural language program such as COBOL... Data FD Master-File. 01 Master-Record. 05 ID PIC X(10). 05 Customer-Fname PIC X(25). . . . Tightly binds the data file and program Output Program

  15. Data Abstraction • Separation between the data’s structure (definition) and the application programs Data and data definitions Database Application Application Application

  16. Advantages of the Database Approach • Reduced redundancy • Data consistency • Greater informational gain • Better access to data and information • Improved data integrity • Improved access and security • Enforcement of standards • Easier modification and updating • Data and program independence • Standardization of data access

  17. Disadvantages of the Database Approach • Complexity • Size • Cost of DBMS • Additional hardware costs • Cost of conversion • Performance • Higher impact of failureStair, 1995

  18. What is a Fourth Generation Language (4GL)? • ...a programming language that is less procedural and more English-like than third generation languages. It emphasizes what is to be done more than how statements are to be written. Stair, 1995

  19. For example... COBOL OPEN INPUT EMPLOYEE-FILE. READ EMPLOYEE-FILE. PERFORM WHILE NOT EOF IF EMP-ID = SEARCH-KEY DISPLAY EMP-ID " " EMP-FIRST-NAME " " EMP-LAST-NAME " " EMP-YTD-PAY END-IF READ EMPLOYEE-FILE END-PERFORM. • Three Control Structures: • Sequence • Iteration • Decision

  20. Control Structures COBOL OPEN INPUT EMPLOYEE-FILE. READ EMPLOYEE-FILE. PERFORM WHILE NOT EOF IF EMP-ID = SEARCH-KEY DISPLAY EMP-ID " " EMP-FIRST-NAME " " EMP-LAST-NAME " " EMP-YTD-PAY END-IF READ EMPLOYEE-FILE END-PERFORM. Sequence

  21. Control Structures COBOL OPEN INPUT EMPLOYEE-FILE. READ EMPLOYEE-FILE. PERFORM WHILE NOT EOF IF EMP-ID = SEARCH-KEY DISPLAY EMP-ID " " EMP-FIRST-NAME " " EMP-LAST-NAME " " EMP-YTD-PAY END-IF READ EMPLOYEE-FILE END-PERFORM. Iteration

  22. Control Structures COBOL OPEN INPUT EMPLOYEE-FILE. READ EMPLOYEE-FILE. PERFORM WHILE NOT EOF IF EMP-ID = SEARCH-KEY DISPLAY EMP-ID " " EMP-FIRST-NAME " " EMP-LAST-NAME " " EMP-YTD-PAY END-IF READ EMPLOYEE-FILE END-PERFORM. Condition False True Decision

  23. What as Opposed to How How to What COBOL OPEN INPUT EMPLOYEE-FILE. READ EMPLOYEE-FILE. PERFORM WHILE NOT EOF IF EMP-ID = SEARCH-KEY DISPLAY EMP-ID " " EMP-FIRST-NAME " " EMP-LAST-NAME " " EMP-YTD-PAY END-IF READ EMPLOYEE-FILE END-PERFORM. SQL SELECT EMP-ID, EMP-FIRST-NAME, EMP-LAST-NAME, EMP-YTD-PAY FROM EMPLOYEE WHERE EMP-ID=1234

  24. Characteristics of 4GLs • User friendly • Less syntax-bound • Fewer programming skills required • Non-procedural • Emphasis is on what (outs are desired) rather than how (programming statements should be written) • Shorter application development time • GUI (graphical user interface) • Incorporate the use of the mouse (point and click) • Involve the use of icons

  25. Characteristics of 4GLs • Function-based • User calls upon pre-programmed functions • Specifies the arguments and parameters which define the scope of the results • Graphical or tabular output • Popular for developing client/server applications • Toted as client/server solutions

  26. Other CharacteristicsApplicable to Today’s 4GLs • Menu driven • Database oriented • Embedded query commands (e.g., SQL) • Retrieval focused • Query capabilities • Human factors designed Martin, 1991

  27. Menu object Graphic background Event-driven command buttons

  28. SQL statement retrieves customer data

  29. 4GLs: Pros and Cons • Good for ad hoc and nonrecurring reporting • One-time information reporting • Good for prototyping and end-user computing (EUC) application development • Discovering specifications (prototyping) • Developing and implementing single-user applications (EUC) • Short learning curve

  30. 4GLs: Pros and Cons • Poor computing efficiency • Not appropriate for • Processing voluminous amounts of data • Transaction processing • Scheduled reporting • Difficult to enforce organizational computing standards • Very difficult to debug • Very difficult to maintain

  31. Oracle Developer • Forms (interactive) • Presenting information and entering data online • Reports (reporting) • Page-oriented display of information • Graphics (charts) • Graphic representation of data

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