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Introduction to Business Computing 8

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Consolidating Rexx previous exam question. Sharing data Permissions ... Grunge F002. Muppet G110. Simpson F022. Smithers G810. Intro to Computing (Week 8) 8 ... – PowerPoint PPT presentation

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Title: Introduction to Business Computing 8


1
Introduction to Business Computing (8)
  • Revision of Last Week Programming
  • Basic Program Structures
  • Input and Output
  • Rexx practical
  • Week 8 Focus
  • Consolidating Rexx previous exam question
  • Sharing data Permissions
  • Introduction to Databases
  • Assignment workshop Spreadsheet problem

2
Consolidating Rexx
  • You can write any program with these structures

Sequential instructions
One or both of the loops
If..Then..Else
(in a Counting loop, something includes
incrementing the counter)
3
Program Approach
  • Decide what the program has to do
  • And what it wont do
  • Break up the problem into manageable chunks
  • Key part of the design process
  • Also need to define communication between the
    chunks
  • Usually in the form of data they share
  • Though best done with explicit messages
  • Analysis is usually from the top down, for
    example
  • Produce headings
  • Print a line for each table
  • Next stage is to write code to build up the line

4
Output
  • Tables problem taught you these main concepts
  • Construct a line before SAYing it
  • Any line can be built up by stages
  • Parts of the line can be forced to a fixed width
    with RIGHT(what, howlong) or LEFT of course
  • Optional example
  • Produce a bar-chart of the first 8 squares
  • Something like
  • 1
  • 2
  • 3
  • 4 ... and so on

5
Parsing Input
  • Simple way to analyse data from the keyboard
  • Parse Pull x y z takes data from external input
    stream and pours it into variables x y and z
  • First token of the input goes into x
  • Next token goes into y
  • All the rest goes into z (note, this time we
    keep spaces)
  • So if you type The quick brown fox
  • x will contain The
  • y will contain quick
  • and z will contain brown fox

6
Experimenting with Parse
  • You can write a program that takes keyboard input
    and plays it back to you in a parsed form
  • Insert some character around output to highlight
    blanks
  • Make the whole thing a loop so it keeps on
    working
  • Provide an escape from the loop!
  • Example
  • Say "Enter lines of text, ending with end"
  • Do Until t1"end"
  • Parse Pull t1 t2 t3
  • Say "gt"t1"ltgt"t2"ltgt"t3"lt"
  • End
  • Note what happens to multiple blanks in your input

7
Arrays
  • Often we want to define a variable that holds a
    series of things
  • For example, could have tables containing name
    and room number
  • On each line, name goes with room
  • If we find name on cell 4 of names…
  • ..room is in cell 4 of room-numbers
  • Most languages let you do this
  • Usually with an index in brackets
  • e.g. Names(i) where i is a number
  • Rexx uses a dot Names.i

8
Previous Exam Question (1)
  • Used stemmed variables (arrays) to hold currency
    names and exchange rates
  • / initialization /
  • ncurr 4 / num of national currencies /
  • currency.0 "euro"
  • rate.0 1 / there is one euro per euro! /
  • currency.1 "UK Pound"
  • currency.2 "US dollar"
  • currency.3 "DM / frCH might be better /
  • currency.4 "FF / and maybe CzK /
  • Now we can ask for rate.1 through to rate.ncurr

9
Previous Exam Question (2)
  • Program was written and tested
  • Then I broke it by changing some statements
  • Each defect generates a different error message
  • You shouldnt find them hard to find and fix
  • Fixing is what programmers do much of the time!
  • To tackle the question, download REXXQ.zip from
    http//cmg.wkac.ac.uk/courses/samples/ and unzip
    it
  • That is, extract the contents of the zip file
  • Text of question is in the handout BS1005w6.doc
    at http//cmg.wkac.ac.uk/courses/bs1005
  • Easy links to both are provided on the BS1005
    home-page
  • Ask if you have a problem

10
Sharing and Permissions
  • Keeping Data Secure

11
Sharing and Permissions
  • For any disk, we want to be able to control who
    can read and write to it and who can assign
    access
  • Owner will normally want full control
  • Users need ability to read and execute
    applications in shared directories
  • Normal users must not erase or change system
    files..
  • .. Or my files!
  • Two basic approaches to permission
  • Passwords
  • User/Group permissions

12
Passwords
  • Password is like a key with it, anyone can get
    in
  • Not secure
  • Everyone requiring access needs to know password
  • It only needs one of them to leak the password
  • Often involves password moving in clear over
    network
  • Tedious
  • Either have to provide password every time..
  • .. or run risk of workstation being taken over by
    another (particularly problematic on remote
    access systems)
  • Windows networking uses an encrypted password
    file
  • You type a password at logon to unlock this file
  • Windows then provides passwords as theyre needed

13
Specific Permission
  • Data owner permits specified people to access
    file
  • Guardian at the gate avoids need for passwords
  • Permits them to run, read, write, delete or
    assign permission
  • Its tedious to have to list every permitted user
  • Therefore collect them into groups
  • Assign permission by group
  • Limit Administrator group (members can do
    anything)
  • Basis of security in
  • Windows NT and Windows 2000
  • System/390 mainframes RACF on MVS and VM
  • Unix systems (including Linux)

14
How it Works at KAC
  • Large servers own most disk storage on campus
  • Most user and application disks are on HOMESERV
  • Desktop machines contain space for the Operating
    System and working storage
  • User logon provides Create/Write/Read/Delete
    access to that users share on the server
  • Also provides Read access to system resources
  • K-drive contains Microsoft Office etc.
  • Server holds both ITCS-supported and other
    software

15
Databases
  • Introduction
  • (You will get more detail next semester)

16
Why use a database?
  • Its difficult to find information in
    unstructured data
  • Hierarchical organization helps analogous to
    putting letters into a file folder
  • Card index is traditional means to hold
    structured data
  • Cards are sorted according to key
  • Structure of other data isnt really exploited in
    normal cards
  • Structuring usually into records and fields
  • Record consists of fields for each category of
    information
  • Address-book fields could be name, address,
    phone, fax...
  • Databases extend sorting to any defined field
  • Structuring address lets you sort on town,
    postcode etc.

17
Simple databases
  • All databases exist to help one collect, organize
    and retrieve data
  • Simplest form is Flat File database
  • This consists of a single table in one DOS file
  • one record per row
  • one column per field
  • Usually offers
  • sorting by any column where this has any
    meaning
  • form view helps you input data and look at
    detail
  • list view to summarize or print multiple
    records
  • Examples Works database (from Microsoft, Claris)

18
Limits of Flat files
  • Every record scanned in every sort operation
  • Multiple scans for complex sorting such as Work
    within category within Composer
  • Updates can involve second copy of entire
    database
  • Gets very slow when database size grows
  • Hard to relate different databases, for example
  • Have database of purchases by customer
  • Customers are also on Address database
  • How do we see whats been selling in PO postcode
    area?

PRODUCT CUSTOMER Grommets Bloggs Ltd Wickets P
Vole Inn Zummats Aardvark Co Zummats Bloggs Ltd
CUSTOMER ADDRESS Aardvark Co Banbury OX18
2AI Bloggs Ltd Fareham PO15 1JB P Vole
Inn Heckmondwyke HX13 3PV
19
Relational Databases
  • Consist of Tables or Relations
  • each data element relates the row (record, tuple)
    its in,
  • with the column (field, domain) that describes
    its category
  • Relational Database Management Systems (RDBMS)
    implement SQL (Structured Query Language)
  • SELECT sales.PRODUCT sales.CUSTOMER FROM lttable
    database namegt WHERE sales.PRODUCTGrommet ORDER
    BY sales.CUSTOMER
  • JOIN tables that share a column to produce a new
    one

PRODUCT CUSTOMER ADDRESS Zummats Aardvark
Co Banbury OX18 2AI Grommets Bloggs Ltd Fareham
PO15 1JB Zummats Bloggs Ltd Fareham PO15
1JB Wickets P Vole Inn Heckmondwyke HX13 3PV
20
Spreadsheet Assignment
  • Due next Thursday, November 28 (Week 9)
  • Deliverables
  • Succinct and focused initial specification,
    stating what the system will do and what it will
    not do (10)
  • Clear description of the initial design proposed
    (20)
  • Project report (25) including
  • The final spreadsheet produced (25)
  • (paper diskette)
  • Bonus for ambitious projects (20)
  • A simple project would get 10 marks
  • Fantastic complexity won't earn more than 20
  • Safer to do a simple job well than a complex one
    badly!

21
Project report
  • Your report should include
  • how the project was broken down into subsections,
  • how the sections were developed,
  • what experimentation or testing was undertaken,
    and
  • what problems were met and how they were overcome
  • Reflective summary of how far you got with the
    project
  • Gives you a chance to say what other things youd
    have done given sufficient time
  • Dont go crazy
  • its only worth 25 of half the module marks
  • 500-750 words should suffice
  • No penalty or credit for overlong reports
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