Introduction to Computer Software

1. Chapter 3 Introduction toComputer Software

3. Software in General • each information system is based upon software under the form of programs and procedures • software is needed for input , processing , output, storage and management activities Trends in software development: • usage of packages • usage of non-procedural languages ( 4GL )

4. Software Categories O’Brien 88

5. Software Trends O’Brien 89 First Generation Second Generation Third Generation Fourth Generation Fifth Generation? Trend: Toward Conversational Natural Programming Languages. User-Written programs Machine language Packaged programs Symbolic languages Operating systems High-level languages Database Management Systems 4GL Microcomputer Packages Natural Languages Multipurpose GUI Expert Software Trends Trend: Toward Easy-to-Use Multipurpose Application Packages.

6. Application Software for End Users • General Applicable Software • suites • MS-office: word , excel, powerpoint, access, outlook, explorer • Web-browsers • netscape • explorer • Electronic mail • CASE • Encyclopedia • Databases • Groupware • Lotus notes Text: O’Brien p 92 - 101

7. Interfaces HW - user O’Brien 98 End user • System software • operating system: OS, DBMS, comm • support: system utilities • development: compilers, CASE, 4GL • Application software • packages • own development Application SW System SW Computer- hardware

8. Operating Systems • User interface • file management • Task management • UNIX, VM or MVS, VSM, MS-DOS • Database Management systems • ORACLE, Informix, INGRES, SYBASE, DB2, Paradox • Telecommunication monitors • network servers, front-end processors, middleware • Programming languages and Compilers • procedural vs. non-procedural, 4GL, natural languages • Programming Tools • workbenches, prototyping tools, editors, debuggers

9. Basic Functions of an Operating System User interface Communication between system and user Utility management Task management File management Supporting programs and other functions Management of peripheral devices Virtual memory Task follow-up Multitasking Management of data and programs Supporting functions Text: O’Brien p 105

10. Operating System Examples : UNIX, DOS, OS/2, MVS Text- processors Programming languages UNIX Program interpreter Kernel provides elementary computer functions System interface Shell File - and Directory systems Programs Communication and networks Programming- utilities

11. Operating systems Operating system = management system • hides hardware details for the users • different machines look identical • depends on the type of applications

12. Other System Software • Network management ( middleware, firewalls, …) • File management • Database management systems • performance monitors • security monitor Text: O’Brien p 108 - 109

13. Program Interaction with the Environment . permanent dialogue between program and user . input of data in function of the results . moment in time and speed are extremely important for the user (real time) . user friendly ( error messages ) Batch: . no interaction with environment . required data are prepared in advance . results are delivered to the user afterwards . moment in time and speed are unimportant for the user Interactive:

14. The absolute binary loader A program must first be loaded in central memory and the P-register must be initialized with the address of the first instruction of the program. The absolute binary loader is a small program that: . loads the binary form of the program (absolute object code) from the peripheral memory into the central memory . is mostly stored in a reserved part of the memory central memory ABL

15. The "command interpreter" Command interpreter Program that gives access to tables containing the name of the program and its address in the mass memory These tables are managed by the file manager With an instructive command processor the user inputs via the terminal , the name of the program to be executed central memory Load chess chess FMGR comm.int ABL

16. ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ control ________________________ unit The interrupt handler Normal program termination Program X cmnd interpreter return to cmnd.int In case of a program interruption cmnd interpreter Program X return to cmnd.int

17. Task scheduling Task scheduler , job scheduler , queue manager manages the waiting queue of all commands which have not yet been executed If there is space available in memory , the task scheduler selects a task from the input queue and orders the loader to load the corresponding program into the memory Selection criteria . round robin algorithm: FIFO + limited time slice preempted tasks after t sec finished tasks CM new tasks

18. Task scheduler 2 Handle batch queue only if the interactive queue is empty interactive tasks interactive queue finished tasks preempted tasks after t sec CM new batch tasks Batch queue

19. Process scheduling The process scheduler is the part of the operating system that decides which program in memory , the CPU will work on . Process status's task terminated active transition active-waiting start i/o load wait for CPU i/o terminated blocked (interrupt) swap-out Transition Active-Waiting after action of the process scheduler

20. Process priorities Algorithm for according priorities must be : - simple ( overhead ) - give I/O jobs higher priority for optimal usage of I/O active select process with P max P:=P-1 wait for CPU blocked P:=P+1 P can get an initial value , eg. depending on the user category

21. Spooling In case of shared usage of peripheral equipment in a multi-programming environment Part of the operating system that writes all of the available input and output per program on a disk , and makes it available as soon as the required peripheral equipment is free . Spooling monitor: Program A Program B spooler Program C disk

22. End-User Applications • general purpose packages • word processing , productivity packages • Application-specific programs • Business application programs • Scientific application programs • Education, entertainment, art, law, medicine, ... • Graphics packages • Integrated Packages

23. Programmingandprogramming languages

24. Programming The same hardware can be used for various applications thanks to the programmability • Specific aspects of tasks are not build-in in the hardware • but in the software . They are loaded in the program memory • ( except for some I/O functions ). • Programming is an important aspect in every automation project. • The programmer has to know the problem very well ; • this has to be achieved during analysis or specification gathering . • Specifications are focused on the user. • Specifications are reflected in programs and translated into • an executable program.

25. Programming Languages A Programming language is a set of conventions that allows to express a program in a format that is also more or less readable for humans. Machine languages • Use binary coded instructions Assembly languages • use symbolic coded instructions Higher Programming languages • use statements that are close to English together with arithmetic notations Fourth generation languages • use natural and non-procedural statements Object oriented languages • Data and procedures are combined in objects

26. Elementary Languages There is a direct relationship between the vocabulary of the language ( syntax ) and the instructions for the computer The most elementary language is the machine language - operation codes and operands have the format of binary numbers - completely machine-dependent - almost unreadable for programmers - source of errors - time consuming - 11011011 represents ADD in a certain language

27. Assembly Languages e.g.: opening door 0 0 KFL D2 D2 D1 D1 D2 1 - - 0 10 KDA 1 3 207 - D1 P2 D2 P3 P3 P4 D2 P5 D2 P6 D1 P7 P3 P8 P1 P9 DDA P1 1 2 3 4 5 6 7 8 9 STO STO EQ? MUL ADD ADD NE? NE? STO • Operation codes and operands get symbolic names • Addresses of words in memory that contain data • get a meaningful name • Require important knowledge about computers • susceptible to errors • Still hardware related

28. Higher Level languages In higher level programming languages they try in the first place to make abstraction of the used machine • Procedures and data are described in terms that are closer to the application domain in which they are used • An instruction can represent a set of machine instructions ; Variables can take abstract values eg.: month • Much higher productivity; • lower risk for errors: • Imperative languages: BASIC, FORTRAN, COBOL, ADA, PASCAL, C, Modula, … • Non-imperative languages: LISP, PROLOG, Scheme

29. Language Example Calculate the average of two numbers Memory addresses: written 30 oral 31 final 40 Pascal: final := ( written + oral ) / 2 Assembler: load a,written (CALM) add a,oral divide a,#2 store a,final machine language: 66 30 54 31 43 02 67 40 required computer knowledge always higher

30. Assessment • productivity of programmers is better with higher programming languages • Translation into machine language is not always optimal leading to theoretically slower programs • Higher cost for computer capacity largely compensated by reduced programming costs • elementary languages only used in case of: - hardware cost much higher than programming cost - small programs sold in large quantities - critical parts of programs for supercomputers

31. Imperative languages With imperative languages the programmer writes all tasks to be performed in the appropriate sequence e.g.: linear equation AX+B=0 - read coefficients A and B ; - calculate quotient of B divided by A ; - change sign of the result ; - assign the value of the quotient to X ; - write the value of X . COBOL, BASIC, ADA , Pascal , Modula , .....

32. Non-imperative languages In non-imperative languages only the relationships between the data are given. The actions to be performed by thee computer are derived from this relationships. The solution of the linear equation can be formulated as follows: - The coefficients A and B can be read - the variable X is defined by X= - B/A to execute the program it is enough to write: write X e.g.: LISP , PROLOG

33. Object oriented languages In Object oriented languages programs pass an instruction to the object to perform the operation. register C++ Eifel Smalltalk JAVA Visual Basic Calculate interest Monthly overview Actual status Design owner calculate status transmit Text: O’Brien p 113

34. Compilers and Interpreters • Programs written in a higher language must be converted into machine language Source code Compiler Interpreter Object code Hardware

35. Compilers and interpreters 2 Compiler: During compilation the entire program is converted into executable OBJECT code. It can be saved and reloaded several times. This is especially useful for larger programs that have to be executed several times without having to be modified. Interpreter: The source code is translated by the interpreter instruction by instruction into machine language and immediately executed. At every execution the translation is redone. This is interesting to debug programs or for small programs using little mass memory. Source code takes much less space than object code.

36. Compilation vs Interpretation Compilation Interpretation execution modifications error messages memory space mass memory fast slow cryptic large unavoidable Slow fast clear small optional