CSC/ECE 517 Fall 2009/wiki3 18 301: Difference between revisions
mNo edit summary |
mNo edit summary |
||
| Line 2: | Line 2: | ||
---- | ---- | ||
The instability of any package can be calculated using the following formula | The ''instability'' of any package can be calculated using the following formula: | ||
I (instability) = Ce / ( Ca + Ce ) | '''I (instability) = Ce / ( Ca + Ce )''' | ||
In this formula: | In this formula: | ||
Ce – the number of other modules that our package requires to operate. In other words, this is an indicator of package independence. | Ce – the number of other modules that our package requires to operate. In other words, this is an indicator of package ''independence''. | ||
Ca – the number of packages that can be viewed as “dependents“, i.e., “depend upon classes within the package”. This is an indicator of package | Ca – the number of packages that can be viewed as “dependents“, i.e., “depend upon classes within the package”. This is an indicator of package ''responsibility''. | ||
Therefore, in order for a package to be completely independent and also stable, it should not be dependent upon other packages. | Therefore, in order for a package to be completely ''independent'' and also ''stable'', it should not be dependent upon other packages. | ||
Using the formula: I = 0 / ( Ca + 0 ) = 0, has the instability of zero. | Using the formula: '''I = 0 / ( Ca + 0 ) = 0''', has the instability of zero. | ||
Respectively, instable or irresponsible packages would have instability of 1 as shown below: | Respectively, ''instable'' or ''irresponsible'' packages would have instability of 1 as shown below: | ||
I = Ce / ( 0 + Ce ) = Ce / Ce = 1 | '''I = Ce / ( 0 + Ce ) = Ce / Ce = 1''' | ||
Revision as of 03:23, 18 November 2009
Topic: Stable Dependencies Principle
The instability of any package can be calculated using the following formula:
I (instability) = Ce / ( Ca + Ce )
In this formula:
Ce – the number of other modules that our package requires to operate. In other words, this is an indicator of package independence.
Ca – the number of packages that can be viewed as “dependents“, i.e., “depend upon classes within the package”. This is an indicator of package responsibility.
Therefore, in order for a package to be completely independent and also stable, it should not be dependent upon other packages.
Using the formula: I = 0 / ( Ca + 0 ) = 0, has the instability of zero.
Respectively, instable or irresponsible packages would have instability of 1 as shown below:
I = Ce / ( 0 + Ce ) = Ce / Ce = 1