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.CUSTOMERFROM lttable
  database namegtWHERE sales.PRODUCTGrommetORDER
  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