Using VCL as an Aspect-Oriented Approach to Requirements Modelling

Abstract

Abstract. Software systems are becoming larger and more complex. By tackling the modularisation of crosscutting concerns, aspect orientation draws attention to modularity as a means to address the problems of scalability, complexity and evolution in software systems development. Aspect-oriented modelling (AOM) applies aspect-orientation to the construction of models. Most existing AOM approaches are designed without a formal semantics, and use multi-view partial descriptions of behaviour. This paper presents an AOM approach based on the Visual Contract Language (VCL): a visual language for abstract and precise modelling, designed with a formal semantics, and comprising a novel approach to visual behavioural modelling based on design by contract where behavioural descriptions are total. By applying VCL to a large case study of a car-crash crisis management system, the paper demonstrates how modularity of VCL's constructs, at different levels of granularity, help to tackle complexity. In particular, it shows how VCL's package construct and its associated composition mechanisms are key in supporting separation of concerns, coarse-grained problem decomposition and aspect-orientation. The case study's modelling solution has a clear and well-defined modular structure; the backbone of this structure is a collection of packages encapsulating local solutions to concerns.

Using UML for Modeling Procedural Legal Rules: Approach and a Study of Luxembourg’s Tax Law

“…Visualization of logical languages. Bottoni et al [3] and Stein et al [27] propose visualizations for OCL, and Amàlio et al [2] -for the Z language [25]. These approaches are not tailored to legal rules and lack means for addressing the information requirements and complexity factors discussed in Section 2.…”

“…(b) To be a resident taxpayer, one must have a Luxembourgish address (L. [2][3]. If such an address exists (L. 4), the taxpayer is deemed resident (L. 5).…”

Aspect-Oriented Model Development at Different Levels of Abstraction

“…The Visual Contract Language (VCL) [2,3] takes an approach to behaviour modelling that is based on design by contract. A VCL model is organized around packages, which are reusable units encapsulating structure and behaviour.…”

“…11(b)) says that a U ser of package U sers 2 is associated with a Session through the relational-edge HasSession. In addition, the diagram includes an invariant HasSessionIfLoggedIn, stating that each session must be associated with a user that is logged-in [3]. Figure 11(c) gives the global behaviour diagram of package Authentication with the global observe operation U serIsLoggedIn, which says whether a user is logged-in or not; this is described using a VCL assertion diagram (Fig.…”

“…Operation Logout says that provided the user status is logged in (pre-condition), then the user status is changed to logged-out (post-condition). Figure 13 presents package Authorisation, which puts two aspects together: Authentication and AccessControl (see [3]). This package defines the observe operation U serLoggedInAndHasP erm, which checks whether a user is logged in and has the right permissions to execute some task; this puts together the observe operations U serHasP erm of AccessControl and U serIsLoggedIn of Authentication.…”