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Software Project Management. Lecture # 6. Outline. Recap of topics from Chapter 23 Remaining topics of Chapter 23 The Software Equation The Make/Buy Decision Outsourcing Project Scheduling (Chapter 24) What is Scheduling? What is Tracking? Project Scheduling - PowerPoint PPT Presentation
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Software Project Management
Lecture # 6
Outline
Recap of topics from Chapter 23 Remaining topics of Chapter 23
The Software Equation The Make/Buy Decision Outsourcing
Project Scheduling (Chapter 24) What is Scheduling? What is Tracking? Project Scheduling Late Software Delivery & Project Deadlines Project Scheduling Principles People and Effort Relationship
Recap – “Software Estimation”
Software project planner must estimate the following important things before the project begins How long it will take? How much effort will be required? How much money will be involved? How many resources will be required?
People Reusable software Software/hardware
Risk consideration In the beginning, project’s scope and feasibility are
determined. The scope helps develop estimates using one or more techniques that fall into 2 broad categories Decomposition Empirical modeling
Recap – “Software Estimation”
Decomposition involves identifying major software function followed by estimates for each
Empirical techniques use empirically derived expressions for effort and time estimation
Software estimation can never be an exact science but use of good historical data and systematic techniques can improve estimation accuracy
The Software Equation
Suggested by Putnam & Myers It is a multivariable model It assumes a specific distribution of effort over life of
s/w project It has been derived from productivity data collected
for over 4000 modern-day s/w projects E = [LOC x B0.333 / P]3 x (1/t4)
E = effort in person-months or person-years B = special skills factor P = productivity factor t = project duration (months or years)
The Software Equation (Cont.) P reflects
Overall process maturity Management practices Extent to which good s/w engg practices are used Level of prog. Languages used State of s/w environment Skills & experience of team Application complexity
Typical values of P P= 2000 - for a real-time embedded s/w P= 10,000 - for telecomm. & systems s/w P= 28,000 for business applications
Value of B increases slowly as “the need for integration, testing, quality
assurance, documentation and management skills grows”. For small programs (KLOC=5 to 15), B= 0.16, for larger
programs (KLOC=more than 70), B=0.39
The Software Equation (Cont.)
Software equation has two independent parameters LOC t
Minimum dev. Time equations derived from software equation tmin= 8.14 (LOC/P)0.43
in months for tmin> 6 months E = 180 Bt3
In person-months for E>= 20 person-months
The Make/Buy decision
Often it is more cost effective to acquire rather than develop a software
Software managers have following options while making make/buy decisions Software may be purchased (or licensed) off the shelf “Full experience” or “partial experience” software
components may be acquired and then modified as needed
Software may be custom-built by an outside contractor to meet specifications
Software criticality to be purchased and the end cost also affect acquisition process
The Make/Buy decision (Cont.)
For each of the discussed acquisition options, the Make/Buy decision is made based on following conditions Will he software product be available sooner
than internally developed software? Will the acquisition cost plus cost of
customization be less than cost of developing the software internally?
Will the cost of outside support (e.g., maintenance contract) be less than the cost of internal support?
Decision Tree
system Xsystem Xreusereuse
simple (0.30)simple (0.30)
difficult (0.70)difficult (0.70)
minorminor changeschanges
(0.40)(0.40)
majormajorchangeschanges
(0.60)(0.60)
simple (0.20)simple (0.20)
complex (0.80)complex (0.80)
majormajor changeschanges (0.30)(0.30)
minorminor changeschanges
(0.70)(0.70)
$380,000$380,000
$450,000$450,000
$275,000$275,000
$310,000$310,000
$490,000$490,000
$210,000$210,000
$400,000$400,000
buybuy
contractcontract
without changes (0.60)without changes (0.60)
with changes (0.40)with changes (0.40)
$350,000$350,000
$500,000$500,000
buildbuild
Estimated path cost
Means 30% probability
Expected value of cost computed along each branch of the decision tree is:
where i is the decision tree path, for example, For Build path
expected cost = 0.30($380K)+0.70($450K) = $429K Similarly, for Reuse path, expected cost is $382K; for Buy
path, it is $267K; for Contract path, it is $410K. So the obvious choice is “to buy”
Decision Tree
ΣΣ (path probability) (path probability)ii x (estimated path cost) x (estimated path cost)ii expected cost =expected cost =
Outsourcing
Acquisition of software (or components) from a source outside the organization
Software engineering activities are contracted to a third party who does the work at lower cost and (hopefully) at higher quality
Software work within the company is reduced to contract management activity
Outsourcing is often a financial decision Positive side
Cost saving can usually be achieved by reducing own resources (people & infrastructure)
Negative side Company loses some control over the software and bears
the risk of putting its fate in hands of a third party
Project Scheduling (Chap. 24 )
Introduction
After the following have been achieved… Process model selection S/w engg. tasks identification Estimation of amount of work & people Risk consideration and knowing deadline
… the task is to create a setup for achieving the software engineering tasks. This setup is called ‘software project scheduling and tracking’
What is scheduling?
An activity that distributes estimated effort across the planned project duration by allocating the effort to specific software engineering task
Creating a network of software engineering tasks to complete the project and assign responsibilities of tasks and timing of tasks
What is Tracking?
Tracking is the process to make sure that all tasks are completed according to assigned responsibility and schedule.
Overview – Proper Scheduling
Proper Project Scheduling requires All tasks should appear in the network Interdependencies between tasks are indicated Effort and timing are intelligently allocated to
tasks Resources are allocated to tasks Closely spaced milestones are provided for
progress tracking
Reasons for late software delivery
Unrealistic deadline established by some one outside the software development group & enforced
Changing customer requirements that are not reflected in schedule change
An honest underestimate of the amount of work and/or resources required
Risks that were not considered at project commencement
Technical difficulties not foreseen in advance Miscommunication among project staff A failure by project management to recognize that
the project is falling behind schedule and a lack of action to correct the problem.
Dealing With Project Deadlines
Aggressive (actually unrealistic) deadlines are a fact of life in software business
If best estimates indicate that deadline is unrealistic Project Manager should
“Protect his/her team from undue (schedule) pressure… and reflect pressure back to its originators.”
Recommended steps for such situations:1. Perform a detailed estimate using historical data from past
projects. Determine effort and time required.2. Use incremental model, develop a strategy that will deliver
critical functionality within imposed deadline, but delay other functionality until later. Document the plan.
Dealing With Project Deadlines
3. Meet the customer and explain why deadline is unrealistic. Explain what is the new time required to complete this project.
4. Offer incremental development strategy as alternative. Offer some options.
We can increase the budget and have bring resources to get this job done in due time. But this contains increased risk of poor quality due to tight timeline.
We can remove some software functions, and provide remaining functionality later.
Dispense with reality and wish to complete software in due time.
By presenting solid estimates and references to past projects, it is likely that, negotiated version option 1 and 2 will be accepted by customer.
Project Schedule (Evolution)
Project schedules evolve over time During early stages of project planning, a
macroscopic schedule is developed This schedule identifies all major process
framework activities and the product functions to which they are applied
As the project proceeds, each entry on the macroscopic schedule gets refined into detailed schedule
Specific tasks are identified to achieve each activity and are scheduled
Project Scheduling - Basic Principles
Compartmentalization Both the product and the process are decomposed into a
number of manageable activities/tasks Interdependency
Interdependencies among decomposed activities must be identified.
Some tasks can be performed in sequence and other can be done in parallel.
Some activities can not be performed without completion of another and some can be totally independent
Time Allocation Each task must be allocated work units (person-days of
effort) Start and end time must be allocated considering
interdependencies
Project Scheduling - Basic Principles
Effort validation Project manager must ensure that no more than the
allocated no. of people have been scheduled at any given time
Defined responsibilities Every scheduled task must be assigned to a specific team
member Defined outcomes
Work products must be defined for every scheduled task Defined milestones
Every task/group of tasks must be associated with a project milestone. A milestone is accomplished after one or more related work products has been reviewed for quality and approved
Relationship of People and Effort
Common Myth … “If we fall behind schedule, we can always add
more programmers and catch up later in the project!”
Doing so is often disruptive rather than productive causing further delays. Reasons: learning time teaching takes time away from productive work added communication paths – increased
complexity
Relationship of People and Effort
Putnam-Norden-Rayleigh (PNR) Curve indicates the relationship between effort applied and delivery time for a software project.
PNR curve was used to derive the software equation
to = delivery time that will result in least effort expended As we move left to to, i.e. as we try to accelerate delivery, curve rises
nonlinearly As we try to reduce accelerate delivery, curve rises sharply to left of td
indicating, project delivery time can not be compressed much beyond 0.75td
As we try further, the project moves into impossible region and failure risk becomes high
Tmin=0.75Td td to Development Time
Effort Cost
Ed
Eo
Impossible
Region
PNR Curve & Software Eqn.
The software equation is derived from the PNR curve
It demonstrates a highly nonlinear relationship between time to complete project and human effort applied to the project
Lines of Code (L) is related to effort (E) and development time (t) as:
L = P x E 1/3 t 4/3
Rearranging the equation E = L3 / P3t4
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