An Aspect-Oriented Approach to
Modeling Pervasive
Dependability Features
Robert France
Department of Computer Science
Colorado State University
University of Oslo, 2005
MDD Research at CSU
• Professors
–
–
–
–
Robert France: modeling, formal methods
Sudipto Ghosh: distributed systems, testing
Jim Bieman: metrics, empirical studies
Indrakshi Ray: security, databases
• Research Scientist: Geri Georg
• Students: Raghu Reddy, Devon Simmonds, Eunjee Song,
Dinh-Trong Trung, Dan Matheson, …
• Model-Driven Development Research Areas
(http://www.colostate.edu/~france)
– Testing UML Models
– Domain-specific modeling using patterns
– Aspect-oriented modeling (AOM)
University of Oslo, 2005
Problem
How do we engineer dependable software systems?
How can we systematically incorporate
pervasive security features into a software
system?
University of Oslo, 2005
Outline
• Motivation
• Overview of Aspect-Oriented Modeling
(AOM)
• Separating Security Features: Modeling
Access Control
• Limitations and Open Issues
• AOM versus AOP
• Conclusion
University of Oslo, 2005
Motivation
• Some factors contributing to complexity
– Designers of dependable systems must address
multiple, competing functional and nonfunctional concerns
– The manner in which an objective is realized or
treated can affect how other objectives are
treated
• Need techniques for balancing functional and nonfunctional objectives
University of Oslo, 2005
Motivation - 2
• A design modularization based on the a
subset of features may result in the
distribution of elements of features across
design modules.
– Design decomposition strategy typically based
on functional features
– Pervasive dependability features (e.g., security,
fault tolerance
University of Oslo, 2005
Motivating Example
• Consider a system that manages information about
clients and resources that is required to protect
access to managed information and to be fault
tolerant.
– A decomposition strategy based on functional concerns
can result in classes representing concepts such as
Resource Management, Resource Repository, Client
Management, Client Repository.
• Decomposition based on functional concepts
results in distributed access control and replication
features
– The classes representing functional concepts will also
include fault tolerance and security functionality
University of Oslo, 2005
An Example
of
Crosscutting
Features
Access control feature
replication feature
University of Oslo, 2005
The problem with cross-cutting
features
• … understanding and changing them!
– Information is distributed
– Maintaining consistency in the presence of changes is
problematic
– Difficult to consider alternative treatments
• Lack of attention to balancing concerns early in
the development cycle can lead to major rearchitecting in later stages of development
University of Oslo, 2005
A solution: Aspect-Oriented
Modeling (AOM)
• Localize crosscutting features
– Eases understanding of crosscutting features
– Eases evolution of features
– Eases replacement of features with alternatives
• Aspect-oriented modeling allows
developers to conceptualize, describe and
communicate crosscutting features
separately
University of Oslo, 2005
Key Concepts
• A concern is a problem and a set of properties that
determines acceptable solutions.
– Concerns are addressed/treated in a design
• A concern solution (or feature) model is a
description of a solution that addresses the
problem represented by the concern
• A feature (description) that is distributed across
the modules of a model is said to crosscut the
model
• An aspect model is a description of a crosscutting
feature.
University of Oslo, 2005
Isolating Crosscutting Features
Crosscutting features can be isolated if
distributed elements have common
structural and behavioral features
– Isolated features can be described as patterns
University of Oslo, 2005
Checks whether
caller can carry out
operation
Performs operation
Stores
authorizations
University of Oslo, 2005
The Access Control Aspect Model
University of Oslo, 2005
instantiation
of
AuthorizationRepository
University of Oslo, 2005
instantiation
of
instantiation
of
AuthorizationRepository
AuthorizationRepository
University of Oslo, 2005
Aspect Models
• (Generic) aspect model: A feature pattern
describing common properties of distributed
elements of a crosscutting feature
• Context-specific aspect model: An
instantiation of a (generic) aspect model
– Instantiating an aspect model essentially
determines where an aspect is to be woven in a
base model
– Similar to defining join points in AOP
University of Oslo, 2005
Aspect-Oriented Design
Modeling
• An AOM design model consists of
– a primary model: reflects core design decisions
– aspect models: each describes a crosscutting
feature
– composition directives: constrain how aspect
models are composed with the primary model
University of Oslo, 2005
A Basic AOM Approach
Model
Composition
Composition
Directives
University of Oslo, 2005
Composed
Model
Composition Process Overview
•
Composition involves
1. Instantiating aspect models to produce contextspecific aspect models
2. Composing context-specific aspect and primary
models
•
Step 2 uses a basic name-based composition
procedure
–
•
Elements in the context-specific aspect are merged
with elements with the same names in the primary
model
Composition directives can be used to override
the default name-based procedure
University of Oslo, 2005
(Generic) aspect model
Context-specific
aspect models
Primary model
University of Oslo, 2005