Architectural patterns are important artefacts containing specialized design knowledge to build good-quality systems. Complex systems often exhibit several architectural patterns in their design which leads to the need of architectural pattern composition. Unfortunately, information about the composition of patterns tend to be vaporized right after the composition process which causes problems of traceability and reconstructability of patterns. This paper proposes a pattern description language that first, facilitates several types of pattern merging operation and second, allows the traceability of pattern composition. More specifically, the approach consists of a proper description of pattern that supports composition operations and a two-step pattern design process that helps to preserve pattern composition information.