Property Value

null if this type is declared in a third-party assembly.
null if this type is an interface or an enumeration.
Otherwise returns this type LCOM numeric value.

The single responsibility principle states that a class should not have more than one reason to change. Such a class is said to be cohesive.
A high LCOM value generally pinpoints a poorly cohesive class. There are two LCOM metrics.

• The LCOM takes its values in the range [0-1].
• The LCOM HS defined by LCOMHS (HS stands for Henderson-Sellers) takes its values in the range [0-2]. A LCOM HS value highest than 1 should be considered alarming.

Here are algorithms used by NDepend to compute LCOM metrics:

• LCOM = 1 - (sum(MF)/M*F)
• LCOM HS = (M - sum(MF)/F)(M-1)

Where:

• M is the number of methods in class (both static and instance methods are counted, it includes also constructors, properties getters/setters, events add/remove methods).
• F is the number of instance fields in the class.
• MF is the number of methods of the class accessing a particular instance field.
• Sum(MF) is the sum of MF over all instance fields of the class.

The underlying idea behind these formulas can be stated as follow: a class is utterly cohesive if all its methods use all its instance fields, which means that sum(MF)=M*F and then LCOM = 0 and LCOMHS = 0.

Recommendations:
Types where LCOM > 0.8 and NbFields > 10 and NbMethods >10 might be problematic. However, it is difficult to avoid such non-cohesive types.
Types where LCOMHS > 1.0 and NbFields > 10 and NbMethods >10 should be avoided. Note that this constraint is stronger (hence easier to satisfy) than the constraint types where LCOM > 0.8 and NbFields > 10 and NbMethods >10.

Reference

IType Interface
IType Members