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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
• 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

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
• 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!
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
• User/Group permissions

12
• 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
• 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
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

Co Banbury OX18 2AI Grommets Bloggs Ltd Fareham
PO15 1JB Zummats Bloggs Ltd Fareham PO15
1JB Wickets P Vole Inn Heckmondwyke HX13 3PV
20
• 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

21
Project report
• 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