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COMP365: DESIGN Information systems architecture


COMP365: DESIGN Information systems architecture Information systems have a generic architecture that can be organised as a layered architecture. – PowerPoint PPT presentation

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Title: COMP365: DESIGN Information systems architecture

COMP365 DESIGN Information systems architecture
  • Information systems have a generic architecture
    that can be organised as a layered architecture.
  • Layers include
  • The user interface
  • User communications
  • Information retrieval
  • System database

Information system structure
LIBSYS architecture
  • The library system LIBSYS is an example of an
    information system.
  • User communications layer
  • LIBSYS login component
  • Form and query manager
  • Print manager
  • Information retrieval layer
  • Distributed search
  • Document retrieval
  • Rights manager
  • Accounting.

LIBSYS organisation
Resource allocation systems
  • Systems that manage a fixed amount of some
    resource (football game tickets, books in a
    bookshop, etc.) and allocate this to users.
  • Examples of resource allocation systems
  • Timetabling systems where the resource being
    allocated is a time period
  • Library systems where the resource being managed
    is books and other items for loan
  • Air traffic control systems where the resource
    being managed is the airspace.

Resource allocation architecture
  • Resource allocation systems are also layered
    systems that include
  • A resource database
  • A rule set describing how resources are
  • A resource manager
  • A resource allocator
  • User authentication
  • Query management
  • Resource delivery component
  • User interface.

Layered resource allocation
Layered system implementation
  • Each layer can be implemented as a large scale
    component running on a separate server. This is
    the most commonly used architectural model for
    web-based systems.
  • On a single machine, the middle layers are
    implemented as a separate program that
    communicates with the database through its API.
  • Fine-grain components within layers can be
    implemented as web services.

Weather system description
A weather mapping system is required to generate
weather maps on a regular basis using data
collected from remote, unattended weather
stations and other data sources such as weather
observers, balloons and satellites. Weather
stations transmit their data to the area computer
in response to a request from that machine. The
area computer system validates the collected data
and integrates it with the data from different
sources. The integrated data is archived and,
using data from this archive and a digitised map
database a set of local weather maps is created.
Maps may be printed for distribution on a
special-purpose map printer or may be displayed
in a number of different formats.
System context and models of use
  • Develop an understanding of the relationships
    between the software being designed and its
    external environment
  • System context
  • A static model that describes other systems in
    the environment. Use a subsystem model to show
    other systems. Following slide shows the systems
    around the weather station system.
  • Model of system use
  • A dynamic model that describes how the system
    interacts with its environment. Use use-cases to
    show interactions

Layered architecture
Data display layer where objects are
concerned with preparing and
presenting the data in a human-
readable form
Data archiving layer where objects
are concerned with storing the data
for future processing
Data processing layer where objects
are concerned with checking and
rating the collected data
Data collection layer where objects
are concerned with acquiring data
from remote sources
Subsystems in the weather mapping system
Architectural design
  • Once interactions between the system and its
    environment have been understood, you use this
    information for designing the system
  • A layered architecture is appropriate for the
    weather station
  • Interface layer for handling communications
  • Data collection layer for managing instruments
  • Instruments layer for collecting data.
  • There should normally be no more than 7 entities
    in an architectural model.

Weather station architecture
UI design principles
  • UI design must take account of the needs,
    experience and capabilities of the system users
  • Designers should be aware of peoples physical
    and mental limitations (e.g. limited short-term
    memory) and should recognise that people make
  • UI design principles underlie interface designs
    although not all principles are applicable to all

User interface design principles
Design principles
  • User familiarity
  • The interface should be based on user-oriented
    terms and concepts rather than computer
    concepts. For example, an office system should
    use concepts such as letters, documents, folders
    etc. rather than directories, file identifiers,
  • Consistency
  • The system should display an appropriate level
    of consistency. Commands and menus should have
    the same format, command punctuation should be
    similar, etc.
  • Minimal surprise
  • If a command operates in a known way, the user
    should be able to predict the operation of
    comparable commands

Design principles
  • Recoverability
  • The system should provide some resilience to
    user errors and allow the user to recover from
    errors. This might include an undo facility,
    confirmation of destructive actions, 'soft'
    deletes, etc.
  • User guidance
  • Some user guidance such as help systems, on-line
    manuals, etc. should be supplied
  • User diversity
  • Interaction facilities for different types of
    user should be supported. For example, some users
    have seeing difficulties and so larger text
    should be available

User-system interaction
  • Two problems must be addressed in interactive
    systems design
  • How should information from the user be provided
    to the computer system?
  • How should information from the computer system
    be presented to the user?
  • Interaction styles
  • Direct manipulation
  • Menu selection
  • Form fill-in
  • Command language
  • Natural language

Direct manipulation advantages
  • Users feel in control of the computer and are
    less likely to be intimidated by it
  • User learning time is relatively short
  • Users get immediate feedback on their actions so
    mistakes can be quickly detected and corrected

Direct manipulation problems
  • The derivation of an appropriate information
    space model can be very difficult
  • Given that users have a large information space,
    what facilities for navigating around that space
    should be provided?
  • Direct manipulation interfaces can be complex to
    program and make heavy demands on the computer

Control panel interface
Menu systems
  • Users make a selection from a list of
    possibilities presented to them by the system
  • The selection may be made by pointing and
    clicking with a mouse, using cursor keys or by
    typing the name of the selection
  • May make use of simple-to-use terminals such as

Advantages of menu systems
  • Users need not remember command names as they are
    always presented with a list of valid commands
  • Typing effort is minimal
  • User errors are trapped by the interface
  • Context-dependent help can be provided. The
    users context is indicated by the current menu

Problems with menu systems
  • Actions which involve logical conjunction (and)
    or disjunction (or) are awkward to represent
  • Menu systems are best suited to presenting a
    small number of choices. If there are many
    choices, some menu structuring facility must be
  • Experienced users find menus slower than command

Form-based interface
Command interfaces
  • User types commands to give instructions to the
    system e.g. UNIX
  • May be implemented using cheap terminals.
  • Easy to process using compiler techniques
  • Commands of arbitrary complexity can be created
    by command combination
  • Concise interfaces requiring minimal typing can
    be created

Problems with command interfaces
  • Users have to learn and remember a command
    language. Command interfaces are therefore
    unsuitable for occasional users
  • Users make errors in command. An error detection
    and recovery system is required
  • System interaction is through a keyboard so
    typing ability is required

Command languages
  • Often preferred by experienced users because they
    allow for faster interaction with the system
  • Not suitable for casual or inexperienced users
  • May be provided as an alternative to menu
    commands (keyboard shortcuts). In some cases, a
    command language interface and a menu-based
    interface are supported at the same time

Natural language interfaces
  • The user types a command in a natural language.
    Generally, the vocabulary is limited and these
    systems are confined to specific application
    domains (e.g. timetable enquiries)
  • NL processing technology is now good enough to
    make these interfaces effective for casual users
    but experienced users find that they require too
    much typing

User interface evaluation
  • Some evaluation of a user interface design
    should be carried out to assess its suitability
  • Full scale evaluation is very expensive and
    impractical for most systems
  • Ideally, an interface should be evaluated against
    a usability specification. However, it is rare
    for such specifications to be produced

Usability attributes
Simple evaluation techniques
  • Questionnaires for user feedback
  • Video recording of system use and subsequent
    tape evaluation.
  • Instrumentation of code to collect information
    about facility use and user errors.
  • The provision of a grip button for on-line user