Effort Estimation

• Review Class 11

• Effort estimation

• General Estimation Model

• COCOMO Model

CEN 4021 Class 12 – 02/21

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Risk Analysis and Planning• Defn: Risk – A problem that has a greater

then 0% but less than 100% probability of occurrence.

• A problem is an event that has a negative value associated with it.

• Risk can be listed, categorized, and potentially managed .

• The earlier risk are handled the better the chance of project success.

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Risk Analysis and Planning cont

Sources of Risk:

• Schedule overrun

• Quality

• Misunderstanding of customer requirements

• Uncontrolled continuous changes of customer requirements

• Unrealistic promises to customers made by overzealous sales people or company execs.

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Risk Prioritization• Defn: Risk prioritization - The activity of ordering

risks based on some criterion or set of criteria.

• Recovery cost – The cost in terms of effort or financial expense to solve a problem should a risk materialize.

• We can define the risk value (RV) as follows:

RV(j) = P(j) X RC(j)

P(j) – the probability of risk item j becoming a real problem

RC(j) – is the recovery cost for the risk item j when it turns into a real problem.

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Risk Prioritization cont

• Defn: Risk Value - A recovery cost that is influenced and modified by another criterion or set of criteria. The probability of the risk turning into a problem is such an influencing factor, and when such a factor is taken into account in modifying the recovery cost, the result is the risk value.

• Defn: Risk mitigation – An activity that may reduce minimize, or totally avoid a risk.

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Risk Mitigation contMitigation Value Cost

• The mitigation cost value is defined as follows:

MVC(k) = P(k) X MC(k)

MVC(K) – mitigation cost value of alternative k

P(k) – probability of failure for alternative k

MC(k) – raw cost of mitigation for alternative k

Mitigation value cost – the cost of risk mitigation after taking into account another criterion or a set of criteria, such as probability of mitigation success

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Effort Estimation

• Software cost and effort estimation will never be an exact science [Pressman 2005]

• There are too many parameters, e.g., human, technical, environmental, and political parameters, that affect the actual estimation making it almost impossible to have considered all cases.

• Even if all parameters are considered, the following questions still need to be answered:

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Effort Estimation cont

1. How much does each parameter contribute to the total effort estimation?

2. How can the amount of each parameter’s contribution be converted into some numerical form?

3. How do the parameters affect each another?

4. How would these effects be combined?

The above point to the fact that there is a lack of good metric definitions related to estimations.

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Effort Estimation cont• Historically, spmrs have based many of their

estimates on some form of “consulting the expert”:

– Consult other peer managers with experience

– Engage consultants with experience

– Draw analogies to past projects that seem to have similar characteristics

– Divide and conquer – break project into components and get estimates for each component based on experience, then combine the estimates

The practice of consulting the experts and using past experience has worked well in the past

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General Estimation Model

• It is important to have as accurate an estimation as possible, since this estimate is used in planning the schedule and resources.

• Several researchers have constructed effort and cost estimation models. To date these models have produced mixed results.

Software effort estimation model: A set of information and relationships organized for the purpose of estimating the effort needed to complete a s/w project. The information and the values assigned to the information may vary from project to project.

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General Estimation ModelSoftware effort estimation model cont:

Similarly, the relationships may be organized into a mathematical equation, which may vary from project to project.

Most models use the following general form, or its derivative, to estimate effort:

Effort = (a + [b x (Sizec)]) x PROD(f’s)wherea, b, c = statistically derived coefficients or best approxs.Size = estimated size of the project f’s = factors that influence the project estimatesPROD(f’s) = the product of arithmetically multiplying those

factors

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General Estimation Model cont

• The coefficients a, b, c were derived by fitting the best curve against known data for the Effort and Size parameters for previous projects.

• Effort is usually measured in terms of person-months expended on the project.

• Size is usually the number of lines of code created as part of the project.

• The Size metric is itself a problem! If it is measured in terms of “lines of code” (LOC), then there must be clear definition and agreement on LOC.

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General Estimation Model cont

• How do you define LOC?

– Should LOC include only executable code?

– What about documentation of code?

– Is an LOC written in assembler the same an LOC in C++ or JavaScript?

– How do we account for the difference between an LOC in assembler language code and an LOC in an HLL?

• More recently function points have been introduced as a possible alternative for the Size parameter.

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General Estimation Model cont

• Estimates the amount of functionality.

• How do you define a function point (FP)?

1. A value is assigned to each of five attributes: inputs, outputs, inquires, master files, and interfaces. Represents five functional components of a s/w product and each is assigned a weight. The weighed attributes are summed to give an initial estimate of function points called the unadjusted function point.

2. Fourteen factors related to the s/w are used to adjust the initial estimate. These factors include considerations such as portability, reusability, performance criteria, and distributed data needs.

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General Estimation Model cont

• How do you define a function point (FP) cont?

2 cont: Each factor is assigned a value ranging from 0 to 5. The sum of the values of these factors is multiplied by 0.01 plus a constant value of 0.65. (?) The sum, which is called the total complexity factor, may range from 0.65 to 1.35.

3. The function point is computed by multiplying the adjusted function point and the total complexity factors. One may view the function point estimate of s/w as the adjusted function point estimate that has experienced a 14-factor adjustment.

See example on handout.

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General Estimation Model contOther Factors affecting Project Effort

• The effort required for a project also depends on the conditions under which the project is being undertaken.

• These conditions include among others:– Programmer productivity

– S/w support services e.g., levels of testing e.g., 3 levels (functional, component, system) vs. 2 levels (functional, system)

– Maturity of the organization, working with an established process.

– Type and amount of tool support

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General Estimation Model cont• All the preceding factors, the f’s in the general

estimation equation, affect the project.

• It is a good idea to have a standard list of factors to be considered during estimation. This list will:

– serve as a reminder

– bring some consistency to what the spmrs consider

• The list of factors (f’s) may also be interrelated. The question of how to account for the combined effects of all these factors continues to be a perplexing challenge.

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The COCOMO Effort Estimation Model

• The COnstructive COst Model (COCOMO) is a specific example of the general estimation equation developed by Boehm in the 1980’s.

• COCOMO includes 3 levels of models:

1. A macro estimation model

2. An intermediate-level model

3. A more detailed micro estimation model

• The intermediate model is used in the example in the text.

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The COCOMO Model cont

General process of using the COCOMO is:

1. Choose an estimate of what would be considered the “nominal” (typical) development of the project. Three nominal project modes are defined: Organic, Semidetached, and Embedded.

2. Choose an estimate of the size of the project to use the Size parameter.

3. Review the factors that influence the project, the cost drivers, and estimate the influence that each factor will have on the chosen “nominal” case.

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The COCOMO Model cont

General process of using the COCOMO is cont:

4. Determine the effort for the s/w project by inserting the estimated values into the Effort Formula.

Nominal Mode of Development

• The following key project characteristics are used to identify one of the three nominal models:

A. The teams understanding of the project objective

B. The teams experience with similar or related projects

C. The project’s need to conform with the est. reqs.

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The COCOMO Model cont

D. The project’s need to conform with the established external interfaces

E. The need to develop the project concurrently with new systems and new operational procedures

F. The project’s need for new and innovative technology, architecture, or other constraints

G. The project’s need to meet or beat the schedule

H. The project’s size range

• Organic mode – projects are fairly easy and familiar to the s/w development team.

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The COCOMO Model cont

• Semidetached mode – projects are medium sized and some what familiar to the s/w development team.

• Embedded mode – complex projects that may be unfamiliar to the project team.

• The above summary statements should be used as a starting point in the decision process when choosing the most appropriate mode for the project estimate.

See Table on next page (Table 17.1 in text)

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Key project charac.

Organic mode Semidetached mode Embedded mode

A Detail degree Considerable degree

Only general degree

B Extensive amount Some amount None to modest amount

C Only the basic ones Considerably more than the basic ones

All and full conformance

D Only the basic ones Considerably more than the basic ones

All and full conformance

E Little to some Moderate amount Extensive amount

F None to minimal Some Considerable

G Low Medium Must

H < 50,000 delivered LOC

50,000 to 30,000 delivered LOC

All sizes

Table 17.1 Mode of the Development Use in COCOMO

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The COCOMO Model cont

• An untrained spmr might not be able to easily choose the correct mode.

• Very few projects have characteristics that fall neatly within any one of the mode categories.

• For each of the three modes, a different formula is used for estimating the Effort:

Organic: Effort (in person-months) = 3.2 x (Size)1.05

Semidetached: Effort (in person-months) = 3.2 x (Size)1.12

Embedded: Effort (in person-months) = 3.2 x (Size)1.20

Size is expressed as LOC.

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The COCOMO Model cont

• Estimating lines of code early in the project may be difficult. Therefore some estimation techniques use function points.

• The new COCOMO II offers the following estimation model:

Effort = 2.45 x (Size)m x PROD(f’s)

Here Size may be either function points or LOC.

PROD(f’s) is a product of several factors that influence the project

m varies in value depending on the project situtation

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The COCOMO Model cont

• If the project is large and there is a lot of communication and integration overhead, then m > 1.

• If the project has a high potential for savings due to better tools, better processes, or better people, then m < 1

• If the project has neither great overhead or great savings then m = 1.

• A set of 15 factors, cost drivers, influence the project.