Fractal is a modular and extensible component model that can be used with various programming languages to design, implement, deploy, and reconfigure various systems and applications from operating systems to middleware platforms and graphical user interfaces.

The Fractal component model makes heavy uses of the separation of concerns design principle. The idea behind this principle is to separate the various concerns or aspects of an application into distinct pieces of code or runtime entities. In particular, the Fractal component model uses three specific cases of the separation of concerns principle: namely separation of interface and implementation, component-oriented programming, and inversion of control.

The first pattern corresponds to separation of design and implementation concerns. The second pattern corresponds to the separation of the implementation concern into several smaller composable concerns, implemented in well-separated entities called components. The last pattern corresponds to the separation of the functional and configuration concerns: instead of finding and configuring themselves the components and resources they need, Fractal components are configured and deployed by an external, separated entity.

A Fractal component is composed of two parts: content that manages the functional concerns and a membrane of controllers that manages zero or more non-functional concerns (introspection, configuration, security, transactions, etc.). The content is made up of other Fractal components, i.e., Fractal components can be nested at arbitrary levels. The introspection and configuration interfaces that can be provided by the controllers allow components to be deployed and reconfigured dynamically. These control interfaces can be used either programmatically or through tools based on them, such as deployment or supervision tools.

Conclusion
Computer science is entering a new generation. The emerging generation starts by abstracting from software and sees all resources as services in a Service Oriented Architecture. In a world of services, it's the service that counts for a customer, not the software or hardware components that implement the service. Service Oriented Architectures are rapidly becoming the dominant computing paradigm. However, current SOA solutions are still restricted in their application context to being in-house solutions. A service Web will have billions of services. While service orientation is widely acknowledged for its potential to revolutionize the world of computing by abstracting from the underlying hardware and software layers, its success depends on resolving a number of fundamental challenges that SOA doesn't address today.

We showed in this article how we're going to help realize a world where billions of parties are exposing and consuming services via advanced Web technology. The outcome of this work will be a comprehensive framework and infrastructure that integrates complimentary and revolutionary technical advances into a coherent and domain-independent service delivery platform:

• A distributed registry to store semantic information about services.
• A dynamic composition engine based on autonomic extension to a BPEL engine.
• A service policy enforcement mechanism that takes into account policies enforcement as specified in the SLA contract.
• A lightweight service infrastructure providing distributed ubiquity thanks to a peer-to-peer architecture.

References
Studer et al. Semantic Web Services Concepts, Technologies, and Applications. Springer. 2007.

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