Reuse%20Revisited

1
Reuse Revisited

• A reminder of basic software reuse gauging
  techniques and additional topics.
• Ernest Cachia
• (As part of CSA404)

2
Lets Remember

• Bankers coarse estimate of reuse percentage
  and reuse leverage
• Poulin-Carusos estimate of
• reuse cost avoidance
• reuse value added
• additional development cost
• a projects return on investment value
• Balda-Gustafsons effort cost estimate based on
  the COnstruction COst MOdel (COCOMO)
• (Selected slides from CSM203 could be reviewed at
  this point)

3
The Benefits of Reuse(in theory)

• Lower development costs
• Higher product quality
• Higher production rate
• Reduced development process time
• Lower failure/defect risk
• Lower personnel training costs
• Easier (clearer and cleaner) maintenance
• Enhanced interoperability

4
The Benefits of Reuse(in practice - example 1)

• Nippon Electric Company (NEC)
• Basic reuse of 17 translated to
• Productivity 6.7 times (over 1 year)
• 10.4 times (over 7 years)
• Software quality 2.8 times (over 1 year)
• 8.5 times (over 7 years)
• Domain(s) Basic and communication switching
  systems
• (1996 data)

5
The Benefits of Reuse(in practice - example 2)

• Toshiba Corporation
• Basic reuse of 60 translated to
• Defect reduction 28 (over 1 year)
• Software quality 4.3 times (over 1 year)
• Domain(s) Control and communication systems
• (1992 data)

6
The Benefits of Reuse(in practice - example 3)

• DEC
• Basic reuse of 50-80 translated to
• Productivity 3-5 times (over 1 year)
• Software quality 2.3 times (over 1 year)
• Domain(s) Computer control systems
• (1994 data)

7
The Benefits of Reuse(in practice - example 4)

• Hewlett-Packard (HP)
• Basic reuse of 70 translated to
• Defect reduction 50 (avg. over 2 projects)
• Productivity 45 (avg. over 2 projects)
• Timeliness 43 (avg. over 2 projects)
• Domain(s) Basic and computer peripheral control
• systems
• (1995 data)

8
The Benefits of Reuse(in practice - example 5)

• Raytheon Corporation
• Basic reuse of 60 translated to
• Productivity 50 (over 2 COBOL projects)
• Defect reduction 44 (over 2 COBOL projects)
• Domain(s) Large-scale information systems
• (1980 data) - One of the very first sightings
  of commercial reuse then
• hailed as a major trend for the future
  but not quite ripe for its
• time!

9
The Benefits of Reuse(in practice - example 6)

• Software Architecture Engineering, Inc. (SAE)
• Basic reuse of 80-90 translated to
• Productivity 54 (over 3 C projects)
• Defect reduction 39 (over 3 C projects)
• Domain(s) Distributed software applications
• (1992 data)

10
The Benefits of Reuse(in practice - in general)

• Study of 75 Ada projects in 15 firms (30 MLOC in
  all)
• Software quality (all aspects) increased by an
  average of 10 times in relation to just 10-18
  reuse levels. (1991-92 data)
• Study of 9 major software producing companies
  practising reuse
• Defect reduction 58
• Project cost ?84
• Timeliness 70 (all over 1 year 1994-95)

11
Main Reuse Model Types

• Reuse level models (a post-mortem static analysis
  - How much has been reused?)
• Reuse leverage models (a post-mortem comparative
  analysis - How has reuse improved a given
  activity?)
• Reuse economic models (a predicative estimate
  composed of a combination of 3 basic approaches)
  see slide 14

12
Reuse Level

• Very popular (widespread use)
• Easy to relate to
• Easy and quick to calculate
• Widely adopted industry standard metric
• Reused software
• Reuse x 100
• Total software
• Note that the above is meaningless without a
  count object definition

13
Reuse Leverage

• Not as popular as the reuse level metric
• It is a comparative metric
• Easy and quick to calculate
• Based on productivity
• Productivity with reuse
• Leverage
• Productivity without reuse
• E. g. If RL for ORGa is 1.35 this means that
  ORGa has increased its productivity by 35

14
Reuse Economic Models

• Cost Avoidance (CA - estimate - How much money
  will be saved?)
• Return On Investment (ROI - estimate - Will
  money be saved in the long-run?)
• Cost-Benefit (C-B - estimate - Should reuse be
  considered at all?) see cost and benefit
  breakdown tables on separate handouts.

15
Frakes-Terry Reuse Level Metric

• More detailed then the Banker metric
• Specifically targeted at C (but can be re-applied
  with basic assumptions)
• The basic reusable object, referred to as an
  item, is generally considered to be a function
  (as in C)
• Differentiates between internal and external reuse

16
Frakes-Terry Definitions

• The main definitions
• ETL (External Threshold Level) - The number of
  times an external item must be invoked before
  considering an invocation as reuse.
• ITL (Internal Threshold Level) - Same as ETL but
  for an internal item.
• EU (External Usage) - Usage of items over and
  above ETL.
• IU (Internal Usage) - Usage of items over and
  above ITL.
• T (Total) - Total number of items in system both
  internal and external.

17
Assumptions for the Frakes-Terry approach

• No internal reuse (this is usually the case as
  items generated by a team are taken to be items
  included in application development and not
  reused). Therefore
• ITL ? ?
• and it follows that IU ? 0
• Any invocation of external items is taken to be
  reuse. Therefore ETL ? 0

18
Frakes-Terry Reuse Level Relationships

• Internal reuse level IU / T
• External reuse level EU / T
• Total reuse level (IU EU) / T
• Values range from 0 (i.e. no reuse) to 1 (i.e.
  system made up solely of reused items)
• Please note that the actual size of an item
• in the Frakes-Terry approach should
• always be taken into account. A complexity
• weighting should be used within the metric
• if straightforward LOC is not used.

19
Frakes-Terry Example

• The actual example will be discussed during
  lecture sessions. However, the initial
  conditions/assumptions of the example are shown
  on this slide.

External items
Internal items
Main item 15 LOC
Item C 20 LOC
Item D 10 LOC
Item A 25 LOC
Item B 30 LOC
Item E 25 LOC