1. CQML: Aspect-oriented Modeling for Modularizing and Weaving QoS Concerns in Component-based Systems
Sumant Tambe*
Akshay Dabholkar
Aniruddha Gokhale
Vanderbilt University, Nashville, TN, USA
*Contact :
16th Annual IEEE International Conference and Workshop on the Engineering of Computer Based Systems (ECBS),
San Francisco, CA, USA

2. Component-based Enterprise DRE Systems
Characteristics of component-based enterprise DRE systems
Multiple reusable components composed together to realize functionality
Simultaneous Quality of Service (QoS) requirements
E.g., Availability, Network quality of service, Timeliness
Examples of Enterprise DRE systems
Advanced air-traffic control systems
Continuous patient monitoring systems
Add yellow box stating goal of RT FT in EDRE.

3. QoS Design Challenges
System’s structure is the primary design dimension whereas QoS is the secondary
Challenges
QoS requirements often cross-cut the structural dimension
E.g., deciding the number of replicas and their interconnections in a fault-tolerant system
Low-level imperative techniques of specifying QoS are overly complex
E.g., API calls for configuring object request broker (ORB) for real-timeliness
Multiple QoS interact in complex ways, which is extremely hard, if not impossible, to analyze at code level
Granularity of applicability of QoS varies widely
E.g., System level, component assembly level, component level, component connection level, port level, method level
QoS notations tightly coupled with platform-specific modeling languages

4. Solution: Declarative Modeling of QoS Requirements
Desirable properties of a graphical QoS modeling language for Component-based Systems
Platform-independent representation of QoS
High-level, declarative QoS specification
Separate “structural view” and “QoS view” for separation of system design concerns
Fine to coarse granularity of QoS association
Reusable, Extensible
Decoupled from structural meta-model to enable independent meta-model evolution
If it is decoupled from the structural meta-model, it would be more reusable.
Our solution: Component QoS Modeling Language (CQML)

5. High-level Declarative QoS Modeling using CQML
CQML is developed using GME
FailOverUnit
Annotate protected components and assemblies
Specify # of replicas
Network-level QoS
Annotate component connections
Specify priority of communication traffic
QoS provisioning using differentiated services
Security QoS
Annotate component ports or connections
Controls role-based access control (RBAC) Policies
More QoS can be added

6. Separation of Concerns
Separate Structural view from the QoS view
CQML model interpreters and transformations coalesce both the views of the model
We’ll see how this separation of concerns is important in case of fault-tolerance.

7. Granularity of QoS Associations
QoS view supports different granularity
Components
Connections
Component Ports
Component Assemblies
Interface Methods
Granularity is based on the feature model of contemporary component modeling languages
Examples of contemporary component modeling languages
PICML for CCM platform
J2EEML for J2EE platform
ESML for Avionics platform

8. Composition of CQML and Base Languages
CQML uses a base language with the features shown before
Added as a library in base language using GME meta-model composition
Does not disturb syntax, semantics, and interpreters of the base language

9. Composition of CQML and Base Languages
Language composition similar to MOF’s import + inherit
CQML join-point model defines a set of abstract structural elements
Join-point model is reused by inheriting it in the concrete structural elements of the base language
Reuse of associations, cardinalities, and constraints defined over the abstract elements
CQML’s
Join-point model

10. Superimposing Declarative QoS Aspects
Dependency Inversion Principle (DIP) applied at meta-modeling level
All concrete QoS elements inherit associations from abstract elements
Reuse of associations, cardinalities, and constraints defined over the abstract elements
Abstract QoS elements correspond to abstract structural elements
CQML’s
Join-point model
Abstract QoS Elements
Concrete QoS Elements

11. Using CQML for M2M Transformation
Automated Structural FT Modeling
Composite Metamodel
CQML

12. Using CQML for M2M Transformation
Problem: Generating replica components using CQML’s FailOverUnit modeling
Step1: Model structural composition of components
Step2: Annotate components with FailOverUnit(s) marking them “protected” in the QoS view
Step3: Use aspect-oriented M2M transformation developed using Embedded Constraint Language (ECL)
Step4: Component replicas and interconnections are generated automatically
Step5: Use existing interpreters of the base language to generate platform-specific metadata.
Transformation
QoS View
Structural View

13. Concluding Remarks
Separation of structural and QoS concerns is key to simplifying system design with non-functional requirements
CQML provides higher level graphical QoS modeling support (e.g., fault-tolerance)
CQML enhances a structural modeling language with declarative QoS modeling capability when composed
CQML separates QoS design from structural design using views
Aspect-oriented M2M transformations can transform QoS requirements into structural models automatically

14. Thank you!