ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE) Volume 3, Issue 3, March 2014 156 All Rights Reserved © 2014 IJARCSEE SOFL - A Better Approach for Formal Specification: A Case Study Based Comparison Muhammad Babar Yaqoob Khan, Sadaf Anwar, Nasir Mehmood Minhas University Institute of Information Technology PMAS Arid Agriculture University Rawalpindi, PAKISTAN Abstract— Formal Methods are necessary for the specification, development and verification of safety critical systems. Formal Languages help us to identify errors at an early stage in the development process and can aid in reducing overall system development costs. Despite their benefits, formal methods are not widely accepted in the industry due to the need for high abstraction and a mathematical labor pool. The SOFL (Structured Object-Oriented Formal Language) methodology can be effective and efficient for safety critical systems. Some major issues with formal languages like higher abstraction levels, the need of mathematical skills, developer maturity and high costs can be overcome by using SOFL. SOFL specifically encapsulates three major layers: 1) structured methodology in the early stage of development, 2) object oriented methodology at the detailed level and 3) incorporation of formal methods. In this paper, we have tested the SOFL 3-step approach for the formal specification of a Railway Signaling System, already implemented by using Zed. Afterward we performed a comparison, using certain parameters identified from literature, to assess the appropriateness of Zed and SOFL methodology for the formal specification of a safety critical system. We found SOFL as an instinctive and perceptive for formal specification which overcome the limitations of other formal languages. Keywords— SOFL; Formal Specification; Railway Signaling System; Formal languages. I. INTRODUCTION The Structured Object-Oriented Formal Language (SOFL) is a sort of Formal Language which basically started at the University of Manchester, UK in 1989. SOFL was completed at the Hiroshima City University and it was settled down at Hosei University in 2000. SOFL is new for the Safety Critical systems. It has been used for the information systems, mostly [1][2]. SOFL has been finalized with the assortment of Vienna Development Method (VDM), Petri Nets and Data Flow Diagrams (DFD) [3][4]. The challenges of formal languages are: specifications of large-scale and complex software systems, it can be difficult to understand and to write. The second major issue is communication between client and developer because formal methods used the mathematical notations due to this, modifications become time-consuming and costly. The last issue is the tool support which does not necessarily reduce the difficulty of formal methods usage. The target of SOFL is to handle all above issues. SOFL is based on three major steps. The first step is Informal Specification. Informal specifications are identified after taking requirements from the users in an informal way. Then do functional analysis. This is a compatible and informal pace. The second step is Semi formal Specification which is formed from the informal system specification. SOFL 3-Step Approach figure:01 Inspiration taken from [6] The third and last step of this three step approach is Formal Specification but before that CDFD (condition data flow diagram) need to be developed and on the basis of formal design, formal specification is gathered. Later on verification, validation, implementation, review and testing has been performed [5].