  Measuring software maintainability early in the development life cycle,
especially at the design phase, may help designers to incorporate required
enhancement and corrections for improving maintainability of the final
software. This paper developed a multivariate linear model 'Maintainability
Estimation Model for Object-Oriented software in Design phase' (MEMOOD), which
estimates the maintainability of class diagrams in terms of their
understandability and modifiability. While, in order to quantify class
diagram's understandability and modifiability the paper further developed two
more multivariate models. These two models use design level object-oriented
metrics, to quantify understandability and modifiability of class diagram. Such
early quantification of maintainability provides an opportunity to improve the
maintainability of class diagram and consequently the maintainability of final
software. All the three models have been validated through appropriate
statistical measures and contextual interpretation has been drawn.
