Harel, D. On Visual Formalisms. CACM, 31(5), pp. 514--530, May 1988.  Home/Search   Document Details and Download   Summary   ACM   TOC   Related Articles   Check

....system by removing ambiguity. In general, speci cation languages can be classi ed into two categories. One is for the speci cation of behaviors, and the other for the speci cation of properties. There exist many behavioral speci cation languages based on various formalisms including automata[1], Petri nets[2] and process algebra[3] theories. Their goal is to describe precisely how a system changes. On the other hand, the goal of property speci cation languages is to capture what the system should ful ll in a declarative style. Due to their higher abstraction, it is a common practice ....

HAREL, D. : `On visual formalism,' Comm. of ACM, May, 1988, pp. 514530

....to capture all relevent aspects of a proposed software system. Usually this paradigm is embodied in a single requirements language, such the Software Requirements Engineering Methodology s (SREM) RSL [2] 3] SADT [4] 5] CORE diagrams [6] RML [7] entitydataflow diagrams [8] or statecharts [9]. While these languages have been carefully designed to suit the purposes of requirements development, two obstacles restrict their usefulness: 1) each language s limitations make it inconvenient or impossible to express some important requirements, and (2) software developers already have a ....

D. Harel, On Visual Formalisms, Comm. ACM 31 (5), 514-530 (1988).

....Applying Wittenburg et al. s visualisation would simply show a large number of cross reference nodes with no detailed indication of how they group with each other across the other hierarchies. A further system that could represent overlapping classification information is Harel s Higraphs [79]. Rather than being a computer based visualisation, Higraphs are manual diagram constructions, much like Venn Diagrams, for visualising structures with properties associated with both sets and graphs. The basic approach is to draw nested and intersecting sets as in a conventional Venn Diagram and ....

Harel, D. (1988). On Visual Formalisms. Communications of the ACM, 31 (5), 514-530.

....on performance, reliability, or performability studies. Most real systems, however, exhibit complex behaviors which cannot be captured by simple models having a small or regular state space. Given the high expressive power of formalisms such as Petri nets [24, 23] queueing networks, state charts [17], and ad hoc textual languages [14] the correct logical behavior can, in principle, be modeled exactly. The timing behavior is then de ned by associating a probability distribution to the duration of each activity. The resulting stochastic process can be solved by discrete event simulation. ....

D. Harel. 1988. On visual formalisms, Comm. of ACM, 31(5), 512-530.

....vehicle throughout this thesis. The second concept the approach presented in this thesis is based on is that of finite state machines and their graphical representation, state transition diagrams. The Swiss mathematician Leonhard Euler (1707 1783) was the first using graphs as a visual formalism [Harel88]. Graphs are defined as a set of points or nodes connected by edges or arcs. State transition diagrams are graphs where the nodes represent states and the directed arcs represent states changes caused by events. The nodes are called states and the arcs transitions. A state transition diagram is ....

....communication. Since the number of states of a system grows exponentially when the system grows linearly, statecharts are a powerful tool in specifying the dynamic behavior of reactive systems. Statecharts are not only a tool for visualization but are based on a clear mathematical formalism ([Harel88]) and, hence, the graphical concept of statecharts is called visual formalism. As already stated, a state diagram is the visual counterpart of a finite state machine. To implement the dynamic behavior of a system programmers often hard code finite state machines using large, multipart ....

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Harel D., "On visual formalisms", Comm. ACM, 31, pp.514-539, 1988

....of queries described in Section 2.2. Also, we describe how to construct a valid visual query expression and to evaluate its semantics. 3. 1 VOQL At a Glance: Query Primitives, Syntactic Grammar, and Semantics VOQL is built on visual query primitives from a visual notation called the Higraph[15] which combines the advantages of the graph and the Venn diagram. As the first look at a visual query expression, let us consider Figure 3 to visualize the query Example 2.1. A query diagram in VOQL interprets the visual query primitives such as blobs and edges from the extensional view of a ....

Harel, D., "On Visual Formalisms," In Communications of the ACM,Vol.31, No.5, pages 514--530, 1988.

....design. Consequently, the implementation of these features tends to compromise the integrity of the layers. We developed a new component model, which we call the mode component model. In this model, a designer specifies the component s interface using a variant of Harel s StateChart formalism [8, 9]. Like a traditional component model, the interface to a mode component defines a collection of services, each of which can be invoked by a component at a higher level in the layering hierarchy. An interface under the mode component model, however, also associates temporal and functional ....

D. Harel. On visual formalisms. Commun. ACM, 31(5), 1988.

....most promising, since such languages allow for much better integration with the CASE tools and a smoother transition from design into implementation [Mes94] There are two major families of visual languages derived from CASE tools. One family of visual languages is based on extended state diagrams [Har88, Emb92]. These languages can have expressive power equivalent to text based languages and are especially good for expressing concurrency. However, their hard readability and difficulty in dealing with complexity seriously restricts their wide acceptance. Another family is based on extended ....

Harel, D. "On visual formalisms," Communications of the ACM, 31(5):514-530, 1988.

....and reading. Special interest is devoted to the revisions of the knowledge base caused by reading and writing. The instantiations of the proposed abstract structure are contextand situation dependent. 2. An ecient mechanism for formal diagrammatic representation of semantic networks are higraphs [7], which integrate two types of relationships in topological diagrammatic formalisms. These are binary relations represented in graphs and structural relationships among sets known from Venn diagrams. Additionally higraphs can also represent the Cartesian product. A drawback of this formalism is ....

Harel, D. (1988), On Visual Formalisms, Communications of the ACM, 31/5, 514-530.

....to those errors. The Error Detection and Recovery Specifications centered around abstract finite state machine definitions. Finite state machines have been the center of many specification efforts. Perhaps the most well known specification methodology for finite state machines is Statecharts [33]. Statecharts are a formalism for hierarchical finite state machines, implemented in a software package called Statemate. Statecharts are basically finite state machines augmented with hierarchy, parallelism, and modularity. An extension to Statecharts, Requirements State Machine Language (RSML) ....

Harel, D. "On Visual Formalisms," Communications of the ACM, Vol. 31 No. 5, May 1988, pp. 514-530.

....diagram. The underlying data structure to be visualized in our approach is a kind of 2D network of components and relationships. Each component is part of exactly one composition and compositions can be higher level components as well. Therefore our object model can resemble the Higraph structure [Hare88] or hierarchically clustered networks [Sch 96] When generating views, this explicit hierarchy of objects will be used by the visualization algorithm (see section 5) to determine how detailed each element will be displayed. The definition of the Adora language is yet not fully complete. However, ....

Harel, D.: On Visual Formalisms. Comm. of the ACM, Vol. 31, No. 5; May 1988. (pp. 514-530)

....attention. Hammer 1995, p. 10) However, as a consequence of his detailed examination of the formal properties of those graphical systems, he is able to indicate how each of these types are related to each others. For instance he observes that the system of higraphs introduced by David Harel in (Harel 1988) is an extension of Euler circles. Euler circles represents subsets of a domain with closed curves, and higraphs basically extends this feature with the ability to represent binary relations between these subsets using arrows. Any Euler diagram is accordingly also a higraph. Similarly any Euler ....

Harel, David (1988): "On visual formalisms", Communications of the ACM, 31.

....two basic types of components, nodes and links or edges . Nodes are used to represent a wide variety of entities, ranging from the extremely abstract to the concrete, and the links are used to represent many kinds of relationship including those that are structural, temporal, causal or functional [8]. There are many variations of node link diagrams, but most commonly, the nodes are drawn as rectangular boxes, or circles, and the edges are lines or arrows that connect the nodes. Graphs, as used by mathematicians and theoretical computer scientists are generally very abstract structures of ....

Harel, D., (1995) On Visual Formalisms, In J. Glasgow, N.H. Narayanan, and B. Chandrasekaran, Diagrammatic Reasoning: Cognitive and Computational Perspectives, MIT Press. 235-272.

....some graphical notation. However, the imprecise semantics of most current OO methodologies and graphical techniques often leads users and analysts to ambiguous interpretations, causing errors in the early stages of the life cycle that can be critical for the rest of the development. To quote Harel [19], unless these pictorial notations are backed up by precise semantics, they remain only pretty pictures. An important goal is to combine the intuitive appeal of visual notations with the precision of formal specification languages. Despite their negative aspects (e.g. learning difficulties or ....

....to achieve this kind of formal verification we will focus on the fulfillment of the orthogonality property for any given UML Statechart diagram. 4: Proving properties: the orthogonality example Orthogonality is the dual of the OR decomposition of states, being in essence, an AND decomposition [19]. Intuitively, orthogonality requires that being in a state, the system must be in all of its AND components. Therefore, each transition defined in a UML Statechart diagram must preserve the orthogonality defined in the system and fulfil it along the full state hierarchy. In order to suitably ....

D. Harel, "On Visual Formalism", Comm. of the ACM, vol. 31 (5) 1.988.

....of the integration of applications. State Charts are also part of UML (Unified Modeling Language) 31] the emerging standard for modeling of applications, hence, together with XML, provide a solid basis for our work. We give below a brief overview of State Charts. For detailed description see [24, 25]. A state chart is a higraph (see [25] consisting of rounded rectilinear blobs representing states, possibly nested and linked by transitions. A simple state chart is shown in Figure 5. The state names, when significant, are written in the small rectangle attached to the top of the state (e.g. ....

....Charts are also part of UML (Unified Modeling Language) 31] the emerging standard for modeling of applications, hence, together with XML, provide a solid basis for our work. We give below a brief overview of State Charts. For detailed description see [24, 25] A state chart is a higraph (see [25]) consisting of rounded rectilinear blobs representing states, possibly nested and linked by transitions. A simple state chart is shown in Figure 5. The state names, when significant, are written in the small rectangle attached to the top of the state (e.g. Search Activity, ShoppingCart Activity, ....

D. Harel. On visual formalisms. Comm. Assoc. Comput. Mach., 31(5):514--530, 1988.

....of probes to the implementation which allows it to be diagnosed as it runs. Such tools are only available very late in the development process, when much, if not all of the code is available. But there are well developed techniques for giving suitably abstract descriptions of intended behaviour [3, 5, 14, 15]. Most of these are based on some variation of the finite state machine (or statetransition chart) wherein components are viewed as having state which undergoes change as a consequence of transitions. By choosing sufficiently abstract states to model, transitions can be both simple to describe ....

D. Harel, "On Visual Formalisms," Communications of the ACM, 1988.

....Cluster tree of the clustered graph in Figure 1. Clustered graphs were introduced by Feng [6] as a model for relational structures with a node hierarchy. There are many closely related models; for example, the compound graphs of Sugiyama and Misue [16, 14] are more general; the higraphs of Harel [8] are far more general. We need two elementary operations for clustered graphs. C create cluster(S: set of nodes) creates a new cluster of the set S of nodes, and returns an identifier for the new cluster. As a precondition, Eades and Huang, Navigating Clustered Graphs , JGAA, 4(3) 157 181 ....

D. Harel. On visual formalisms. Commun. ACM, 31(5):514--530, 1988.

....tools to model data using the Entity Relationship approach (see 48 J. P. KELLER AND R. PAIGE [16] or OMT; see [67] They are also used to define functional specifications with Data Flow diagrams (see [91] and to develop real time specifications in a synchronous system model by Statecharts; see [42]. Case tools used within these software engineering approaches also have an informal capability to transform these initial specifications. In particular, it is standard nowadays for integration testing applications to be hand derived with machine assistance from the kinds of semi formal ....

Harel, D., On visual formalisms, CACM 31, No. 5, 1988, pp. 514--530. 60 J. P. KELLER AND R. PAIGE

....can however use appropriate analysis and design methodologies with the aim of testing. In some work, design models are used to help testing procedural software. Particularly, finitestate machines are used in [Chow 1978, Waeselynck 1993, Thvenod Fosse et al. 1995] for testing purpose. Statecharts [Harel 1988], an extension of finite state machines producing modular, hierarchical, and structured descriptions are also used to model behavioural aspects of a software : in [Thvenod Fosse Waeselynck 1993, Waeselynck 1993] the authors use Statemate, a tool based on Statecharts [Harel et al. 1990] for ....

D. Harel, "On Visual Formalisms", Communications of the ACM, 31, pp.514-30, 1988.

....This has the advantage of being accessible to people with a less mathematical background, while being sufficiently expressive and formal. A further consideration was that some BAe engineers are already familiar with the notation through experience of the Statemate tool [6] Statecharts [7, 8, 9, 6] are an extension of state machines and state diagrams for the specification of reactive systems. Timed Statecharts [10] take this further to deal with time constraints. S1 S2 [l,u] ev2 E ev1 Figure 1: Example of a simple timed statechart Each box in the diagram represents a system state, ....

D. Harel, "On visual formalisms," Communications of the ACM, vol. 16, no. 4, pp. 514--530, 1988.

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D. Harel, "On visual formalisms," Comm. Assoc. Comput. Mach., vol. 31, no. 5, pp. 514--530, 1988.

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Harel D (1988) On visual formalisms. Comm ACM 31:514-530

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Harel, D. On Visual Formalisms. CACM, 31(5), pp. 514--530, May 1988.

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D. Harel. On visual formalisms. Commun. ACM, 31(5):514-- 530, 1988.

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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Harel, D. 1988. On visual formalisms. Communications of the ACM 31(5):514--530.

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Harel, D.: On visual formalisms. Comm. of the ACM 31 (1988) 588--600

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Harel, D., 1988. On Visual Formalisms. Communications of the ACM 31, 514-530.

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Harel, D., 1988. On Visual Formalisms. Communications of the ACM 31, 514-530.

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Harel, D.: On visual formalisms. Comm. of the ACM 31 (1988) 588--600

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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Harel, D., 1988. On Visual Formalisms. Communications of the ACM 31, 514-530.

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D. Harel, "On Visual Formalisms," Communications of the ACM, Vol 31, No 5, pp. 514-530, May 1988.

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D. Harel. On visual formalisms. Comm. of the ACM, 31(5):588--600, 1988.

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D. Harel, 1988, "On Visual Formalisms," Communications of the ACM, 31(5), pp514--530.

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D. Harel. "On Visual Formalisms." Comm. of the ACM, 31(5):514--530, May 1988.

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D. Harel. On visual formalisms. CACM, 31(5):514--530, May 1988.

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D. Harel, `On visual formalisms', Communications of the ACM, 31, (5), 514--530 (1988).

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D. Harel, "On Visual Formalisms," CACM 31(5), pp. 514--530, 1988.

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D. Harel, `On visual formalisms', Communications of the ACM, 31, (5), 514--531 (1988).

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D. Harel. "On Visual Formalisms", Communication of the ACM. Vol. 31, No. 5, 1988, pp. 514-530.

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HAREL D. (1988), "On Visual Formalism", Communications of the ACM, volume 31, number 5, page 171-187.

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HAR88 Harel, D. On Visual Formalisms. CACM 31:514-530 1988.

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D. Harel, "On Visual Formalisms," Comm. ACM, May 1988, pp. 514-530.

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Hare1 1988 Harel, D., "On Visual Formalisms," 31, no. 5, pp. 514-530, May, 1988.

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