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Application Development in Fourth Generation Systems

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Fourth Generation SystemsObjectives: to speed up the application building

process to reduce maintenance costs by making

the application quick and easy to modify to make languages user friendly so that

users can solve their own problems Also: to incorporate the latest advances in

development techniques & technology to achieve the above

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Fourth Generation Development

Users and developers collaborate Usually an Iterative DevelopmentIterative Development

the system is described graphically a prototypeprototype is built based on the design evaluation and refinement of design a second and third build may be required final testing and deployment

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Fourth Generation Development...

Involves: Client / Server Development Event Driven Programming Graphical User Interface (GUI)

Development Object-Oriented Programming (and

reuse) Database Transaction Processing

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The Application Developer must know:

how to manage a database a query language (SQL & embedded SQL) system development methodologies rapid prototyping of applications

Rapid Application Development Client / Server concepts GUI / Windows concepts OO programming

performance tuning of the application transaction management with

concurrency and locking strategies

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Developing a 4GL Application

Visual Programming Environment with an interactive dialogue structure

Software Engineering Support interactive testing interactive debugger code/objects reuse multiple developers configuration management

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Interactive Dialogue Structure: Screen interaction via form-filling Leads the developer (with Help and

validation) Offers menu choices, lists, function keys... Default Options (developer can change

default) Two dimensional

(developer can click on an object, move a cursor or scroll an image ...)

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Client / Server Concepts

Client / Server Systems Client / Server Systems are are decomposed into three elements: servers, clients & the links between them

Server:Server: provides a clearly defined set of services & a

documented interface for activating those services Client:Client:

requests services; processes, then displays the results

Linkage:Linkage: based on telecommunications links or calls within the

same processor

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Client / Server Concepts ...Client / Server ConnectionsClient / Server Connections Open SystemsOpen Systems

the interfaces used within the system adhere to international standards

Distributed SystemsDistributed Systems can be categorized by what is distributed:

processing, data or both OOOO

objects are like servers or clients with a message interface

Most common is the PC-style workstation Most common is the PC-style workstation connected over a LANconnected over a LAN or WANor WAN

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Client / Server Concepts ...

Application Development TiersApplication Development Tiers Presentation Layer - GUIs Business Rules or Application Logic Database Layer

2-Tier2-Tier Fat Server - data and business rules Fat Client - GUI and business rules

3-Tier or 3-Tier or nn-tier-tier each layer on its own

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Client / Server Concepts ...4GLs and Client / Server4GLs and Client / Server

At the Presentation Layer most 4GLs concentrate on the interface

At the Business Rules Layer the business logic may be coded in the client

application, be in stored database procedures and triggers or be in a separate tier

At the Database Layer use wizards to generate the database

4GL Trends - 3-Tier, Distributed, OO, GUI4GL Trends - 3-Tier, Distributed, OO, GUI

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GUI / Windows Concepts

User Interface DesignUser Interface Design Ultimate goal is EASE OF USE Features

Real world metaphors Selection rather than remembering Consistency User control Feedback Forgiveness Perceived stability

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GUI/Windows Concepts ...A well designed screen

can improve productivity by 25%

Principles of Good Screen DesignPrinciples of Good Screen Design All screens in the system should look and

act consistent Cohesion:

Each screen should do one complete task

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GUI / Windows Concepts ... Cohesion

Only data relevant to the task is on the screen Build screen L->R, Top -> Bottom Screen contents should be balanced,

symmetrical Horizontal division of data better than vertical Use no more than 25% of screen Left justify data fields Use visual highlighting carefully e.g.

high brightness to identify data fields Reverse video can be hard to read, but

useful for errors

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GUI / Windows Concepts ... The Use of ColourThe Use of Colour

Excessive colour can be confusing About 8% of European males are

colour-blind and cannot distinguish red from green

Average users remember the meaning of 5-7 colours so keep the number of colours to 4 giving the brain space for other activities

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GUI / Windows Concepts ... The Use of Colour ...The Use of Colour ...

Avoid combining colours with different perceptual depths

e.g. red advances while blue recedes It is difficult to distinguish

blue lines on black & yellow lines on white

Use common meanings for colours e.g. red: danger, stop yellow: caution, slow green: OK, go

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GUI / Windows Concepts ...

Multiple WindowsMultiple Windows Application design must determine the (WWS)

WWS - Working Windows Set ie the number of windows the user needs in a certain time period to perform the task efficiently

If the WWS cannot fit the screen the user must: search or scroll to find the required window delete windows to make room for the current one

The user is distracted by “non-active” windows e.g. background tasks with activities like printing &

system monitoring

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GUI / Windows Concepts ...

IconsIcons Are being increasingly used in GUI’s to

represent functions Must be recognisable to the user Best for concrete objects, most effective

as a miniature e.g. waste-paper basket = destroy

Note that some symbols have different meanings in different cultures.

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Creating an ApplicationData Model and DataData Model and Data

Design database (done by lecturer) Create database (done by IT Services) Create tables

use SQL scripts or a software tool(Oracle Schema Manager)

Populate the tables with data for testing

use SQL scripts or a software tool(Oracle Enterprise Manager)

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Creating an Application ...

Application DesignApplication Design Develop the application specification

Partition the application for client/server: where will the business rules be coded

Identify the tasks/functions/modules Design the interaction or flow of screens

ie View Navigation Diagram, Screen Hierarchy Chart or Application Flow Diagram

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Creating an Application ...

Application ConstructionApplication Construction Create the application

include library routines and global variables Create each screen

Connect to the database for data access if required

Design the interface layout Set values for interface objects Write code to perform required functions:

normally related to user interaction with interface objects (events)

Compile and test each screen

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Creating an Application ...Application CompletionApplication Completion Test the Application

Integrate all screens Exercise all use-cases Include creation of extra test cases if

necessary Deploy the application

create executables and DLLs, Packages etc

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Terms and Concepts Window

basic visual building block of an application Event

triggered by a user or by code in a script activates a block of 4GL code or script

Script sequence of statements that perform

processing in response to an event e.g. PL/SQL, PowerScript

Control or Interface Object created by the developer to allow user to

interact with the application, or to enhance the interface.

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Tutorial - to be completed by next week

Create the Oracle database tables for your assignment use Oracle Schema Manager (or SQL scripts)

Programs -> Oracle-> OraEMGR -> DBA Management Pack -> Schema Manager)

follow carefully the table definitions given in the assignment, noting primary and foreign keys

Enter data into the tables ensure data conforms to table relationships