This paper examines current approaches to usability metrics and proposes a new approach for quantifying software quality in use, based on modelling the dynamic relationships of the attributes that affect software usability. The Quality in Use Integrated Map (QUIM) is proposed for specifying and identifying quality in use components, which brings together different factors, criteria, metrics and data defined in different Human Computer Interface and Software Engineering models. The Graphical Dynamic Quality Assessment (GDQA) model is used to analyse interaction of these components into a systematic structure. The paper first introduces a new classification scheme into graphical logic based framework using QUIM components (factors, criteria metrics and data) to assess quality in use of interactive systems. Then, we illustrate how QUIM and GDQA may be used to assess software usability using subjective measures of quality characteristics as defined in ISO/IEC 9126.