Relative accuracy of estimates from b boehm
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Relative Accuracy of Estimates ( from B. Boehm ). 4x. Note: we can be “off” by 4 times !. Estimate Range (size/cost). Actual (size/cost). x. .25x. Requirements. Code/Test. Design. Early feasibility. Stages of the Project. More “Modern” version of FP.

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Relative Accuracy of Estimates ( from B. Boehm )

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Relative accuracy of estimates from b boehm

Relative Accuracy of Estimates(from B. Boehm)

4x

Note: we can be “off” by 4 times !

Estimate

Range

(size/cost)

Actual

(size/cost)

x

.25x

Requirements

Code/Test

Design

Early

feasibility

Stages of the Project


More modern version of fp

More “Modern” version of FP

Composed of 3 major steps:

  • Identify and Classifying:

    • Data

    • Transactions

  • Evaluation of Complexity Levels of Data and Transactions

  • Compute the Functional Point


1 identifying classifying 5 basic entities

1. Identifying & Classifying 5 “Basic Entities”

  • Data:

    • Internally generated and stored (logical files and tables)

    • Data maintained externally and requires an external interface to access (external interfaces)

  • Transactions:

    • Information or data entry into a system for transaction processing (inputs)

    • Information or data “leaving” the system such as reports or feeds to another application (outputs)

    • Information or data retrieved and displayed on the screen in response to query (query)


2 evaluating complexity

2. Evaluating Complexity

  • Using a complexity table, each of the 5 basic entities is evaluated as :

    • Low (simple)

    • Average

    • High (complex)

  • 3 attributes are used for the above complexity table decisions

    • # ofRecord Element Types (RET): e.g. employee data type, student record type

    • # of unique attributes (fields) or Data Element Types (DET) for each record : e.g. name, address, employee number, and hiring date would make 4 DETs for employee data stype

    • # ofFile Type Referenced (FTR): e.g an external payroll record file that needs to be accessed


5 basic entity types uses the ret det and ftr for complexity evaluation

5 Basic Entity Types uses the RET, DET, and FTRfor Complexity Evaluation

For -- Internal Logical Files and External Interfacesdata entities:

# of RET1-19 DET20-50 DET50+ DET

1 Low Low Ave

2 -5 Low Avg High

6+ Avg High High

For -- Input, Output and Query transactions:

# of FTR1-4 DET5 -15 DET16+ DET

0 - 1 Low Low Ave

2 Low Avg High

3+ Avg High High


Example

Example

  • Consider a requirement: “has the feature to add a new employee to the “system.”

  • Assume employee information involves 3 external files that each has a different Record Element Types (RET)

    • Employee Basic Information has employee data records

      • Each employee record has 55 fields (1 RET and 55 DET) - AVERAGE

    • Employee Benefits records

      • Each benefit record has 10 fields (1 RET and 10 DET) - LOW

    • Employee Tax records

      • Each tax record has 5 fields ( 1 RET and 5 DET) - LOW

  • Adding a new employee involves 1 input transaction which involves 3 file types referenced (FTR) and a total of 70 fields (DET). So for the 1 input transaction the complexity is HIGH


Function point fp computation

Function Point (FP) Computation

  • Composed of 5 “Basic Entities”

    • input items (external input items from user or another application)

    • output items (external outputs such as reports, messages, screens – not each data item)

    • Queries (a query that results in a response of one or more data)

    • master and logical files (internal file or data structure or data table)

    • external interfaces (data or sets of data sent to external devices, applications, etc.)

  • And a “complexity level index” matrix :

Simple(low)

Complex (high)

Average

3

4

6

Input

5

7

Output

4

3

Query

4

6

Logical files

7

10

15

Ext. Interface

& file

7

5

10


Function point computation cont

Function Point Computation (cont.)

  • Initial Function Point :

    Σ [Basic Entity x Complexity Level Index]

all basic entities

Continuing the Example of adding new employee:

- 1 external interface (average) = 7

- 1 external interface (low) = 5

- 1 external interface (low) = 5

- 1 input (high) = 6

Initial Function Point = 7 + 5 + 5 + 6 = 23

Note that ---- this just got us to Initial Function Point


Function point computation cont1

Function Point Computation (cont.)

  • Initial Function Point :

    ∑ (Basic Entity x Complexity Level Index)

    is modified by 14 DI’s

  • There are 14 more “Degree of Influences” ( 0 to 5 scale) :

    • data communications

    • distributed data processing

    • performance criteria

    • heavy hardware utilization

    • high transaction rate

    • online data entry

    • end user efficiency

    • on-line update

    • complex computation

    • reusability

    • ease of installation

    • ease of operation

    • portability

    • maintainability

These form the 14 DIs


Function point computation cont2

Function Point Computation (cont.)

  • Define Technical Complexity Factor (TCF):

    • TCF = .65 + [(.01) x (14 DIs )]

    • where DI = ∑ ( influence factor value)

  • So note that .65 ≤ TCF ≤ 1.35

Function Point (FP) = Initial FP x TCF

Finishing the earlier Example:

for the example, assume TCF came out to be 1.15,

then Function Point = 23 x 1.15 = 26.45


Function point

Function Point

  • Provides you another way to estimate the “size” of the project based on estimating 5 basic entities :

    • Inputs

    • Outputs

    • Logical Files

    • External Interfaces

    • Queries

  • (note : the text book algorithm is earlier, simplified version)

    (important)

  • ** Then --- still need to have an estimate on productivity

    e.g. function point/person-month

  • ***Divide the estimated total project function points (size) by the productivity to get an estimate of “effort” in person-month or person-days needed.

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