International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 An Engineering Perspective on Structural Computing: Developing Component-Based Open Hypermedia Systems Michail Vaitis, Manolis Tzagarakis and George Gkotsis

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structural Computing: Motivation Inadequacy of information structuring abstractions: –Web applications Links are second class entities Starting-points for unidirectional jumps –Hypermedia applications Employed for incarnating all information structuring situations

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Research on Hypertext Hypermedia domain research –how the human mind perceives structure in different problem domains Hypermedia system research –designing and building the computational foundations to support people working with structure

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Hypermedia domains Hypermedia domain: – a coherent set of structure abstractions that solves a particular data organization problem Navigational Taxonomic Spatial Argumentation support Configuration management Workflow Hyperfiction Linguistics

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Component-Based Open Hypermedia Systems Third-party programs requesting structure functionality Provide domain-specific structure services to clients Fundamental functionality available to all structure servers (persistent storage, naming, event notification control, versioning)

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Architecture of CB-OHS

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structure Server Domain specifications: specifications about the structure abstractions of the domain –Structure syntax Templates / Patterns –Behavior semantics Internal operations External operations Services: Implement the domain-specific interface

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structural Engineering Motivation: the lack of an engineering framework guiding the development process, coupled by the appropriate tools Definition: a systematic and disciplined approach to the development, operation and maintenance of applications and infrastructures that solve structure-oriented problems

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Characteristics of structure servers Structural completeness (structure abstractions should completely solve the structure-oriented problems of the domain) Size (small to medium software projects) Performance (short response time to clients’ request) Distribution and Heterogeneity (operate in a distributed environment of different hardware and software platforms) Specifications evolution (small possibility for the specifications to be changed during the development) Reusability and Extensibility (structure services at a fine granularity level) Life time (long duration of structure services) Robustness, Scalability and Availability (due to a huge number of applications) Introspection capabilities (communicate behavior to other applications) Interoperability (transformation of structures between different hypermedia domain)

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 CB-OHS life cycle

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Scenario description Goals (name of each goal, plus a description of it) Characters (the different kind of users of the service) Data (data examples that may be associated together) Requirements for third party applications (requests) Structure configuration (description and constraints among the structural elements) Behavior description (operations and propagation of them, synchronization among elements) Infrastructure requirements (storage, naming, etc. )  Facilitate discussions among hypermedia application designers and developers  Avoid “reinventing the wheel”.

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structure specifications Syntax –Specification of the structure model of the domain –Contain the basic structural elements, their properties and the connection constraints among them, or to data items –Detection of relevant elements that maybe reused –Structure is a first class entity Behavior –Computational aspects of a domain –Tightly coupled with the structure model Structure syntax and behavior may be considered as different views of the same “whole”, introducing the possibility of specifying both within the same language

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Component implementation Casting of the neutral structural objects stored by the infrastructure, to the specific structure elements concerning the application domain. Abstraction Factory Layer (AFL). Responsible for reifying un-typed structural objects to domain specific abstractions Abstraction Utilization Layer (AUL). The domain specific abstractions may be used by clients

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Deployment and Documentation Structure server in operational mode Clients’ ability to discover and locate the required service Registration of the structure server to the dedicated directory services Configuration of introspection capabilities

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structural Engineering Tools Theoretical armory tools –Aim at supporting problem analysis within the structural computing framework Development tools –Attempt to assist developers when working with CB-OHS

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Theoretical tools and armory Needed primarily by analysts and to a lesser degree by developers Required on two important research fronts: 1.Structural completeness: To what degree structure specifications may cover or solve structural problems? 2.Structural analysis and decidability –Comparison of models and determination of their differences –Decision whether a particular organizational problem belongs to a hypermedia domain, or not

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Development tools 1.Tools for structure model definition Structure specification formalism ─Open to extensions, ─Model-neutral ─Common ground for cooperation 2.Tools for structure behavior specification Modelling dynamic and computational aspects Controlling structure abstractions’ life-span, interaction and reaction to messages

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Development tools (cont’d) 3.Tools for discovering components in CB-OHS –Aim to locate available structure servers without prior knowledge of their existence or their name –Special protocols for browsing structure servers according to certain properties, such as: the name of the domain the interface the structure server is using to receive requests the availability of the server

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Structural computing environments Themis Construct Callimachus

International Workshop on Web Engineering ACM Hypertext 2004 Santa Cruz, August 9-13 Future Work Tools for structural computing –Behavioral modeling Stimulus absorption Propagation of operators –Theoretical armory Structural completeness Structural decidability –Peer-to-peer Hypermedia Structure services discovery