Realizable, Connector-Driven Software Architectures for Practising Engineers

Despite being a widely-used language for specifying software systems, UML remains less than ideal for software architectures. Architecture description languages (ADLs) were developed to provide more comprehensive support. However, so far the application of ADLs in practice has been impeded by at least one of the following problems: (i) advanced formal notations requiring a steep learning curve, (ii) lack of support for user-defined, complex connectors, and (iii) potentially unrealizable architectural designs. This paper proposes Xcd, a new ADL that aims at supporting user-defined, complex connectors to help increase architectural modularity. It also aims to help increase the degree of reusability, as now components need not specify interaction protocols, as these can be specified independently by connectors (which increases protocol reusability too). Connector support requires to ensure that architectural designs are always realizable, as it is currently extremely easy to obtain unrealizable ones. Xcd eliminates potentially unrealizable constructs in connector specifications. Finally, Xcd employs a notation and notions from Design-by-Contract (DbC) for specifying software architecture behaviour. While DbC promotes a formal and precise way of specifying system behaviours, it is not as challenging for practising developers as process algebras that are usually employed by ADLs

A Design-by-Contract based Approach for Architectural Modelling and Analysis

Research on software architectures has been active since the early nineties, leading to a number of different architecture description languages (ADL). Given their importance in facilitating the communication of crucial system properties to different stakeholders and their analysis early on in the development of a system this is understandable. However, practitioners rarely use ADLs, and, instead, they insist on using the Unified Modelling Language (UML) for specifying software architectures. I attribute this to three main issues that have not been addressed altogether by the existing ADLs. Firstly, in their attempt to support formal analysis, current ADLs employ formal notations (i.e., mostly process algebras) that are rarely used among practitioners. Secondly, many ADLs focus on components in specifying software architectures, neglecting the first-class specification of complex interaction protocols as connectors. They view connectors as simple interaction links that merely identify the communicating components and their basic communication style (e.g., procedure call). So, complex interaction protocols are specified as part of components, which however reduce the re-usability of both. Lastly, there are also some ADLs that do support complex connectors. However, these include a centralised glue element in their connector structure that imposes a global ordering of actions on the interacting components. Such global constraints are not always realisable in a decentralised manner by the components that participate in these protocols. In this PhD thesis, I introduce a new architecture description language called XCD that supports the formal specification of software architectures without employing a complex formal notation and offers first-class connectors for maximising the re-use of components and protocols. Furthermore, by omitting any units for specifying global constraints (i.e., glue), the architecture specifications in XCD are guaranteed to be realisable in a decentralised manner. I show in the thesis how XCD extends Design-by-Contract (DbC) for specifying (i) protocol-independent components and (ii) complex connectors, which can impose only local constraints to guarantee their realisability. Use of DbC will hopefully make it easier for practitioners to use the language, compared to languages using process algebras. I also show the precise translation of XCD into SPIN’s formal ProMeLa language for formally verifying software architectures that (i) services offered by components are always used correctly, (ii) the component behaviours are always complete, (iii)there are no race-conditions, (iv) there is no deadlock, and (v) for components having event communications, there is no overflow of event buffers. Finally, I evaluate XCD via five well-known case studies and illustrate XCD’s enhanced modularity, expressive DbC-based notation, and guaranteed realisability for architecture specifications

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018