Exploring Domain-Specific Architectural Description Languages (ADLs)

1. Chapter 6 - Modeling Eduardo Felipe Zecca da Cruz

2. Domain- and Style – Specific ADLs • Some ADLs are domain-specific or style-specific, or at least optimized for describing architectures in a particular domain or style • Importance • Scope is better tailored to stakeholder needs • Unnecessary details could be left because there is little need for genericity • Comprises • A reference architecture, which describes a general computational framework for a significant domain of applications; • A component library, which contains reusable chunks of domain expertise; and • An application configuration method for selecting and configuring components within the architecture to meet particular application requirements.

3. Koala • Developed by Philips Electronics • Specially designed for modeling embedded software for consumer electronics • Inherits from Darwin • Semantically and syntactically • Uses Darwin’s structural concepts of input and output ports • Expands them through the addition of constructs to support product-line architectures • Multiple products can be described with a single model, with differences between the products encoded as variation points

4. Evaluation Rubric for Koala

5. Weaves • Architectural style and accompanying notation. • Used for modeling systems of small-grain tool fragments that process objects of data • Advantages • Extremely optimized notation • Even simpler than Darwin diagrams • Close mapping to implemented systems • Disadvantages • Addresses structure and data flows only

6. Lunar Lander • Components do not communicate by request-response procedure call. They communicate by streams of objects • Basic flows of data are similar to the other models • Explicit presence of return channels for data • A request that travels from a way does not imply that a response comes back along the same way • The response way must be specified • Information about structural connections but does not capture aspects of how those connections are used • Could be included with an additional model like natural language

7. Evaluation Rubric for Weaves

8. AADL • It contains useful constructs and capabilities for modeling a wide variety of embedded and real-time systems such as automotive and medical systems. • Can describe interfaces to components for both the flow of control and data • Can capture non-functional aspects of components such as timing, safety, and reliability attributes

9. AADL Components • Components are defined in two parts • Component type • Defines the interfaces to a component • Component implementation • An instance of a particular component type • Component’s category (additional element that affects components) • Can be hardware, software, or composite

10. More AADL • Advantages • Allows detailed specification of both hardware and software aspects of a system • Automated analysis tools check interesting end-to-end properties of system • Disadvantages • Verbose; large amount of detail required to capture even simple systems

11. Lunar Lander • Just one part is modeling • The Calculation component and its connection to the Data Store component. • The components are connected by a physical Ethernet bus • Real-time version • Activities are done at regular intervals

12. Evaluation Rubric for AADL

13. Extensible ADLs • Can be used to combine the flexibility of generic languages with the analyzability and precision of semantically rich languages. • Provide a basic set of constructs for describing certain common architectural concerns • Include support • Basic approach to employing an extensible ADL is as follows • Determine which concerns can be modeled using the existing (baseline) capabilities of the ADL • For those concerns that cannot be modeled using the baseline capabilities, choose how to extend the ADL to support their modeling (or reuse an extension developed by another user) • Extend the ADL and its supporting tools as necessary to support the modeling of the unique features

14. ACME • Has a base set of seven constructs • Components • Connectors • Ports • Roles • Attachments • Systems • Representations • Properties • Decorations that can be applied to any of the basic seven kinds of elements

15. ACME • Advantages • Structural specification capabilities similar to Darwin • Simple property structure allows for arbitrary decoration of existing elements • Tool support with AcmeStudio • Disadvantages • No way to add new views • Property specifications can become extremely complex and have entirely separate syntax/semantics of their own

16. Lunar Lander • Largely structural and includes components, connectors, ports, roles and attachments • Verbosity • Use of properties • Additional properties could be added using ACME to model Lunar Lander

17. Evaluation Rubric for ACME

18. ADML • XML-based architecture • Syntax derived from ACME • ADML is supported by meta-properties • Advantages • XML parsers and tools readily available • Added some ability to reason about types of properties with meta-properties • Disadvantages • Properties are still name-value pairs • Did not take advantage of XML extension mechanisms

19. Lunar Lander • Similar to ACME • Use of XML opens this specification up to a wider array of tools • Verbose is denser than in ACME

20. xADL • XML-based language • An attempt to provide a platform upon which common modeling features can be reused from domain to domain and new features can be created and added to the language as first-class entities • On the other languages they are added as extensions to other entities

21. xADL • Advantages • Growing set of generically useful modules available already • Tool support in ArchStudio environment • Users can add their own modules via well-defined extensibility mechanisms • Disadvantages • Extensibility mechanisms can be complex and increase learning curve • Heavy reliance on tools

22. xADL Data Binding Library • It is a software library that provides an API for parsing, reading, writing, and serializing documents in a particular language • In xADL it is a set of Java classes that correspond to xADL data types • Data Binding Library provides a simple interface to make these operations (read, write, query, manipulate)

23. Apigen • It is a xADL’s data binding library generator • Given a set of XML schemas, the Apigen can generate the complete data binding library with support for those schemas • For any changes or adds, Apigen will generate a new data binding library by rerunning

24. Lunar Lander • Similar to ADML and ACME • Has an associated graphical visualization provided by an editor called Archipelago • Application can be extended using new schemas and these schemas can be reused in another projects

25. Evaluation Rubric for xADL

26. When Systems Become too Complex to Model • Certain applications cannot be modeled using the techniques that were used on the Lunar Lander example • Gigantic and diverse applications like the Web or Gnutella • Impossible to generate a model of these systems in the traditional components-connectors-and-configuration sense • There are some strategies to consider to model these systems

27. Strategies • Model Limited Aspects of the Architecture • Use Cases • Interaction Patterns • More limited and easier to be modeled • Model an Instance • Consider if a complete model is needed • Modeling only the relevant portion of the system

28. Strategies • Exploit Regularity • Large systems have low heterogeneity • These large portions can be modeled once and repeated automatically • Model the Style • Instead of modeling as an application, consider modeling the REST style instead • WEB is based on the REST architecture • Model the Protocol • Model protocol details • HTTP example on the Web

29. References • Taylor, R. N., & Medvidović, N. (2010).Software architecture: foundations, theory, and practice. Hoboken, N.J.: Wiley. • Modeling and Notations - http://www.softwarearchitecturebook.com/svn/main/slides/ppt/10_Modeling_and_Notations.ppt • Domain-Specific Software Architecture and Product Lines – http://www.csse.usc.edu/classes/cs578_2013/DSSE.ppt