Dorothea Beringer

Conversations + Interfaces = Business Logic

In the traditional application model, services are tightly coupled with the processes they support. For example, whenever a servers process changes, existing clients using that process must also be updated. However, electronic commerce is moving toward e-service based interactions, where corporate enterprises use e-services to interact with each other dynamically, and a service in one enterprise could spontaneously decide to engage a service fronted by another enterprise. We clarify here the relationship between currently developing standards such as UDDI, WSDL, and WSCL, and propose a conversation controller mechanism that leverages such standards to direct services in their conversations. We can thus treat services as pools of methods, independent of the conversations they support. Even method names can be decided on independently of the conversations. Services can spontaneously discover each other and then engage in complicated interactions without the services themselves having to explicitly support conversational logic. The dynamism and flexibility enabled by this decoupling is the essential difference between applications offered over the web and e-services.

CLAM: Composition Language for Autonomous Megamodules

Advances in computer networks that support the invocation of remote services in heterogeneous environments enable new levels of software composition. In order to manage composition at such a high level we envision a need for purely compositional languages. We introduce the CLAM composition language, a megaprogramming language. By breaking up the traditional CALL statement the CLAM language focuses on the asynchronous composition of large-scale, autonomous modules. Furthermore the language has the capability to support various optimizations that are specific to software composition.

A language and system for composing autonomous, heterogeneous and distributed megamodules

New levels of software composition become possible through advances in distributed communication services. We focus on the composition of megamodules, which are large distributed components or computation servers that are autonomously operated and maintained. The composition of megamodules offers various challenges. Megamodules are not necessarily all accessible by the same distribution protocol (such as CORBA, DCOM, RMI and DCE). Their concurrent nature and potentially long duration of service execution necessitates asynchronous invocation and collection of results. Novel needs and opportunities for optimization arise when composing megamodules. In order to meet these challenges, we have defined a purely compositional language called CHAIMS, and are now developing the architecture supporting this language. In this paper we describe CHAIMS and how it meets the challenges of composing megamodules.

A reuse and composition protocol for services

One important facet of software reuse is the reuse of autonomous and distributed computational services. Components or applications offering services stay at the providers site, where they are developed, kept securely, operated, maintained, and updated. Instead of purchasing software components, the customer buys services by invoking methods provided by these remote applications over the Internet. Due to the autonomy of the services, this reuse model causes specific requirements that differ from those where one builds ones own system from components. These requirements have led to the definition of CPAM, a protocol for reusing remote and autonomous services. CPAM can be used on top of various distribution systems, and offers features like presetting of attributes, run-time estimation of costs and having several calls for setup, invocation and result extraction. The CPAM protocol has been successfully used within CHAIMS, a reuse environment that supports the generation of client applications based on CPAM.

A comprehensive model for arbitrary result extraction

Within the realms of workflow management and grid computing, scheduling of distributed services is a central issue. Most schedulers balance time and cost to fit within a clients budget, while accepting explicit data dependencies between services as the best resolution for scheduling. Results are extracted from one service in total, and then simply forwarded to the next service. However, distributed objects and remote services adhere to various standards for data delivery and result extraction. There are multiple means of requesting results and multiple ways of delivering those results. By examining several popular and idiosyncratic methods, we have developed a comprehensive model that combines the functionality of all component models. This model for arbitrary result extraction from distributed objects provides increased flexibility for object users, and an increased audience for module providers. In turn, intelligent schedulers may leverage these result extraction features.

CPAM, A Protocol for Software Composition

Software composition is critical for building large-scale applications. In this paper, we consider the composition of components that are methods offered by heterogeneous, autonomous and distributed computational software modules made available by external sources. The objective is to compose these methods and build new applications while preserving the autonomy of the software modules. This would decrease the time and cost needed for producing and maintaining the added functionality. In the following, we describe a high-level protocol that enables software composition. CPAM, CHAIMS Protocol for Autonomous Megamodules, may be used on top of various distribution systems. It offers additional features for supporting module heterogeneity and preserving module autonomy, and also implements several optimization concepts such as cost estimation of methods and partial extraction of results.