## Вход

Забыли?

#### вход по аккаунту

код для вставкиСкачать
```Tools of the systems analyst
Planning Techniques / Tools
The first stage in the application of a
good planning technique
 is identification of all the activities
which collectively form the project
 and the interdependence of these
activities, desiding which comes first,
and which depends on which, which
This analysis of the tasks helps to
understand project needs and enables
the next vital step to be undertaken:
 estimating the time needed for each
activity (and estimating the time
needed for completing the whole
project).
Techniques for Estimating
 A structured method for accurately
estimating time, costs, and benefits is the
cornerstone for delivering systems on time
and within budget
 Planning and control techniques are only
useful if the estimates are accurate
 “Past experience with similar systems”,
“estimates of experts”, “standards in the
specific area” help us to make better
estimates
Techniques for Estimating
 A specific set of formulas are used to
develop estimates.
 To whatever estimate is arrived at by using
the formulas, we should always consider
existance of the elements beyond our
control (such as unexpectedly high inflation
rate, for instance, can destroy the budget
for a long-term project, and a vendor who
does not deliver equipment on time will put
a project weeks behind schedule).
Techniques for Estimating
One way to incorporate these
unexpected elements into our
estimastes is to apply the standard
requires formulating an optimistic, a
pessimistic, and a most likely
estimate.
Techniques for Estimating
We use these three figures to calculate an
average weighted toward the most likely
estimate:
 WA = (OE) + 4(MLE) + (PE)
6




WA = Weighted average
OE = Optimistic estimate
PE = Pessimistic estimate
MLE = Most likely estimate
Techniques for Estimating
This takes into account unforseen
disasters as well as miracles, without
skewing the estimates too far either
way.
Techniques for Estimating
 A time estimate such as “six months to
build a system” is of little value, since it
gives us nothing against which to check our
progress along the way
 We would not know whether we were
behind schedule until 5 months and 29
days has passed.
 Therefore, when making time estimates, we
break the project down into small chunks
and then predict when each chunk should
be done.
Techniques for Estimating
 By breaking it into pieces, we are better
able to follow the progress (whether we are
behind the schedule) and make more
accurate estimates
 We mark the end of each of the project’s
chunks with a milestone which is a
measurable or verifiable point in time.
 Time charting devices, such as Gantt
Charts and Network Diagrams, are useful to
follow milestones and the progress of the
project.
Techniques for Estimating
 Time estimates should be either in actual
time or elapsed time
 If it is in actual time it is better to transfer
it to the elapsed time
 E. g. : When someone says 1 day job?
What it means? 24 hours (actual time) or
one working day (6-8 hours – elapsed time)
 24 hours is 4 working days (elapsed time)
Time charting devices
 Gantt Charts
 Network Diagrams
 GASP Techniques
Gantt Charts
 The simplest of these techniques is
the Gantt Chart
 Consists of a horizontal bar to
represent each activity in the project
 The length of each bar proportional to
the time that it will take
 The horizontal axis of such a chart
serves as a time scale.
 If shading is used to show completed
activities (either in full or in part), then the
use of a vertical cursor will quickly show
which activities are behind the schedule
 The major advantage of Gantt Charts is
their simplicity, especially the fact that they
show the activities on a direct time base.
 The main disadvantage is that the
interdependence between activities is
not shown
 Although a visual inspection will give
the current status of each activity, it
does not reveal what effect a delay
on one activity will have on the total
project
Main Features of Gantt Charts
 They show activities as bars whose length indicates
duration and position indicates starting time
 They show the sequence of activities and the total
time needed
 They can show the human resources required at each
stage
 They do not show the interdependence between
activities (do not show the critical and non-critical
activities).
 They can show progress to date
 They are simple and easy to follow
 They are easy to prepare
 They can be displayed on A4 sheets
Example
activity
A
B
C
D
E
F
G
H
duration
1
1
10
6
6
3
1
7
predeccessor
A
B
A
D
C, E, H
F
A
Network diagrams
 PERT: Performance Evaluation and
Review Technique
 CPM: Critical Path Method
Network diagrams
 Network diagram techniques were
developed to overcome the fundamental
 They overcome the major disadvantage of
Gantt Charts, by showing the
interdependence of activities
 They also have a major advantage in that
adding the times of the activities on each
route or path between the start and finish
of the project will quickly reveal (show) the
critical path for the project
Network diagrams
Critical path: This is the series of
activities in which any delay will
cause an equivalent delay in the
completion of the project as a whole
– unless corrective action is taken
Network diagrams
 It is also possible to calculate float
time for each activity not on the
critical path
 Float time: That amount of delay
which any activity can incur without
any effect on the final completion of
the project
Limitations of network diagrams
In spite of the major advantages of network
diagrams, it also has some limitations
 First, the current status of the project
cannot easily be seen on the diagram
 Secondly, the preparation of a network
diagram can be time consuming, especially
when there are frequent alterations, even
with the aid of computer software
 Thirdly, a large network diagram is
frequently too complex for use as a
planning document in discussions with
managers
Main Characteristics of Network
Diagrams
 Use arrows and nodes (either circles or boxes) to
show activities
 Show the sequence of activities
 Show the total time needed for the project
 Can not show the human resources required at each
stage
 They clearly differentiate critical and non critical
activities
 Show the logic of the sequences
 They are complex and difficult to follow
 They are difficult to prepare because of calculations
 Need a larger format (than A4) to be displayed on
GASP Technique
 The lack of immediate visual relation to a
time scale is the reason most frequently
quoted for not using network diagrams
 To acquire the advantages of network
diagrams while retaining the advantages of
Gantt Charts, a further technique has been
developed.
 This technique has a number of names
including Job Progress Charting and
Graphical Procedure for Analytical and
Synhetical Evaluation and Review of
Construction Programs (GASP). For
convenience we will refer to the technique
as GASP.
GASP Technique
 Basically a GASP chart may be regarded as
a Gantt Chart which has been extended to
show the relationship between activities.
 Like all other planning techniques, the first
task is to prepare a list of activities and
estimated times for their completion
 The next step is to identify the
interrelationships between the activities on
the list.
GASP Technique
 First a Gantt chart is prepared
 The relationships between activities are
then added to the chart, using vertical lines
to indicate where the end of one activity
represents the commencement of one or
more subsequent events
 Where there is a slack time (float time)
between the completion of one activity and
the start of the next related activity, the
first activity is extended by dotted lines and
linked to the subsequent activity by a
dotted line
GASP Technique
 By adding the relationships to the
chart, all activities for which a time
float exists are thus immediately
identified. The path along which there
is no time float is the critical path
Value of GASP technique
 The GASP technique retains all the
advantages of the Gantt chart (especially
its ability to show easily the current status
of the project and the use of a time scale)
and provides the major advantages of a
network diagram in identifying the critical
path and the relationships between
activities.
 In addition, the learning period for the
GASP technique is considerably less than
that for a network diagram. It is therefore a
useful tool for the planning of a systems
project.
Flowcharts
 A flowchart is a graphic representation of
the steps in the solution of a problem, in
which symbols represent operations, data
flow, hardware, and the sytem plan
 Flowcharts can document either
organizational systems or computer
programs
 Program flowcharts show the sequence of
steps performed in a computer program
 System flowcharts document the overall
system. A system flowchart is a traditional
tool for describing a physical system. It is a
high-level picture of the system
 Flow charting is the symbolism of the
systems analyst
 It enables the analyst to view graphically
partial or complete systems
 It is generally difficult to understand
without diagrams the relationships that
exist within a system
 Flowcharts allow the analyst, systematically
and realistically, to evaluate the current
operations and design new procedures if
necessary
Flowchart symbols
 A standart set of symbols for drawing
flowcharts is used (ANSI = American
National Standarts Institute)
 Flowchart symbols can be used to represent






Functions
Decisions
Actions
Requirements
Inputs/outputs of the system
The equipment used in the system
Flowchart symbols
Process: A process or component that
changes the value or location of data.
Examples include a program, a
processor, and a clerical process
Flowchart symbols
Decision: Indicates a yes/no decision to
Flowchart symbols
Input/Output: Indicates any input or
output
Flowchart symbols
Connector: Indicates an exit to or entry
from another part/page of the chart
Flowchart symbols
Flowline: Used to link symbols. The
flowlines define both sequence and
direction of flow
Flowchart symbols
Terminal point: Marks the beginning or
end of a program or program
segment
Flowcharting rules
The following rules should be followed to when
preparing a flow chart:
 Conventional symbols should be used to
facilitate mutual understanding of the
logical flow of work
 The system, or its components, or both
should have a clearly indicated starting and
halting point in the chart
 The graphic flow of work should always be
in a one direction, normally top to bottom
or left to rigth
Flowcharting rules
 No directional flow lines should be
unconnected at any point. Every directional
line should lead to another step in the chart
 The descriptive statement within any
symbol should be understandable and the
terminology used should be applicable to
the system being studied
 Side notes should be used to provide a
through understanding of the various parts
of the flow charts
Flowcharting rules
 Each decision should have two possibilities:
 A “yes” (positive)
 A “no” (negative
 The flow of the work should be clearly
indicative of what actually happens in the
course of an operation
 Because the flow charting of a complex
system is an involved procedure, it is
recommended that other staff members
associated with the problem participate in
the analysis phase of the flow-charting
operation
Capabilities
A flow chart pictographically representing a
system is uniquely capable of:
 Helping to visualize the system’s
component parts
 It can be utilized as an effective training
device
 Helping in communication about and
understanding the system
 Shows the existing system with all of its
characteristic faults and strengths
```
1/--страниц
Пожаловаться на содержимое документа