Visual notations form an integral part of the language of software engineering (SE). Yet historically, SE researchers and notation designers have ignored or undervalued issues of visual representation. In evaluating and comparing notations, details of visual syntax are rarely discussed. In designing notations, the majority of effort is spent on semantics, with graphical conventions largely an afterthought. Typically, no design rationale, scientific or otherwise, is provided for visual representation choices. While SE has developed mature methods for evaluating and designing semantics, it lacks equivalent methods for visual syntax. This paper defines a set of principles for designing cognitively effective visual notations: ones that are optimized for human communication and problem solving. Together these form a design theory, called the Physics of Notations as it focuses on the physical (perceptual) properties of notations rather than their logical (semantic) properties. The principles were synthesized from theory and empirical evidence from a wide range of fields and rest on an explicit theory of how visual notations communicate. They can be used to evaluate, compare, and improve existing visual notations as well as to construct new ones. The paper identifies serious design flaws in some of the leading SE notations, together with practical suggestions for improving them. It also showcases some examples of visual notation design excellence from SE and other fields.

The “Physics” of Notations: Toward a Scientific Basis for Constructing Visual Notations in Software Engineering

Structures in Other Domains The methodology of structural analysis discussed in this article has been applied beyond the narrow realm of natural language syntax that we have discussed in this article. Within the study of language, similar methods of analysis have been pervasively applied to the study of sounds (phonology), words (morphology), and meanings (semantics), yielding a range of of abstract structural representations whose properties bear considerable explanatory burden. There are a wealth of cases in each of these domains analogous to those discussed here, though space prevents us from going in these (see Akmajian, Demers, Farmer and Harnish 1995 for a traditional overview, and Jackendo 1994 for one more focused on connections with cognitive science). Additionally, these representations have shed substantial light on the processes of language acquisition and language change. It has been found that variation in the types of sentences that are used, whether during the course of children's acquisition of their native languages or in the centuries-long periods of linguistic change, are best characterized not as super cial and haphazard alterations, but rather in terms of parametric modi cations to the fundamental underlying grammatical rules and constraints. Moving outside the domain of language, one application of these same methods has been in the study of music cognition. Just as the representations of linguistic theory arise out of an attempt to model speakers' intuitions about well-formedness and possible meanings of the sentences of their

Structural analysis

In recent years, workflow management systems (WFMSs) have gained popularity in both research and commercial sectors WFMSs are used to coordinate and streamline business processes Very large WFMSs are often used in organizations with users in the range of several thousands and process instances in the range of tens and thousands To simplify the complexity of security administration, it is common practice in many businesses to allocate a role for each activity in the process and then assign one or more users to each role—granting an authorization to roles rather than to users Typically, security policies are expressed as constraints (or rules) on users and roles; separation of duties is a well-known constraint Unfortunately, current role-based access control models are not adequate to model such constraints To address this issue we (1) present a language to express both static and dynamic authorization constraints as clauses in a logic program; (2) provide formal notions of constraint consistency; and (3) propose algorithms to check the consistency of constraints and assign users and roles to tasks that constitute the workflow in such a way that no constraints are violated

The specification and enforcement of authorization constraints in workflow management systems

Object-oriented analysis

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ACM Transactions on Database Systems

Recently, there has been a renovated interest in functional dependencies due to the possibility of employing them in several advanced database operations, such as data cleaning, query relaxation, record matching, and so forth. In particular, the constraints defined for canonical functional dependencies have been relaxed to capture inconsistencies in real data, patterns of semantically related data, or semantic relationships in complex data types. In this paper, we have surveyed 35 of such functional dependencies, providing a classification criteria, motivating examples, and a systematic analysis of them.

Relaxed Functional Dependencies—A Survey of Approaches

An important step in the design of visual languages is the specification of the graphical objects and the composition rules for constructing feasible visual sentences. The presence of different typologies of visual languages, each with specific graphical and structural characteristics, yields the need to have models and tools that unify the design steps for different types of visual languages. To this aim, in this paper we present a formal framework of visual language classes. Each class characterizes a family of visual languages based upon the nature of their graphical objects and composition rules. The framework has been embedded in the Visual Language Compiler–Compiler (VLCC), a graphical system for the automatic generation of visual programming environments.

http://msdl.cs.mcgill.ca/people/hv/teaching/MSBDesign/notes.ClassificationFrameworkVisualLanguages.pdf

A Classification Framework to Support the Design of Visual Languages

We present a framework for modeling visual notations and for generating the corresponding visual programming environments. The framework can be used for modeling the diagrammatic notations of software development methodologies, and to generate visual programming environments with CASE tools functionalities. This is accomplished through an underlying modeling process based on the visual notation syntactic model of eXtended Positional Grammars (XPG, for short), and the associated parsing methodology, XpLR. In particular, the process requires the modeling of the basic elements (visual symbols) of a visual notation, their syntactic properties, the relations between them, the syntactic rules to formally define the set of feasible visual sentences, and a set of semantic routines performing additional checks and translation tasks. Such a process is completely supported by the VLDesk system, which enables the automatic generation of an editor for drawing visual sentences, as well as a processor for their recognition, parsing, and translation into other notations.The proposed framework also provides the basis for the definition of a meta-CASE technology. In fact, we can customize the generated visual programming environment in terms of the supported visual notation, its syntactic properties, and the translation rules. We have used this framework to model several diagrammatic notations used in software development methodologies, including those of the Unified Modeling Language.

A framework for modeling and implementing visual notations with applications to software engineering

We describe a design methodology for iconic languages based upon the theory of icon algebra to derive the meaning of iconic sentences. The design methodology serves two purposes. First of all, it is a descriptive model for the design process of the iconic languages used in the Minspeak? systems for augmentative communication. Second, it is also a prescriptive model for the design of other iconic languages for human-machine interface. An interactive design environment based upon this methodology is described. This investigation raises a number of interesting issues regarding iconic languages and iconic communications.

A methodology and interactive environment for iconic language design

Positional grammars are a formalism for the definition and implementation of visual languages. They have already been used in the past as part of the VLCC system (Visual Language Compiler-Compiler) for the definition and the implementation of visual environments for editing and compiling flowcharts, chemical structures, combinatorial networks, electric circuits, etc. The authors introduce the eXtended Positional Grammars (XPG) that enhance the descriptive power of positional grammars. We also present a more powerful LR based methodology for parsing visual languages described by XPGs. The result is the possibility of describing and compiling a much wider class of visual languages, yet keeping most of the LR parsing efficiency.

Giuseppe Polese

Papers

Relaxed Functional Dependencies—A Survey of Approaches

A Classification Framework to Support the Design of Visual Languages

A framework for modeling and implementing visual notations with applications to software engineering

A methodology and interactive environment for iconic language design

Extended positional grammars