Modularizing Crosscutting Concerns in Component-Based Systems

Abstract

We define a method to modularize crosscutting concerns in the Behavior Interaction Priority (BIP) component-based framework. Our method is inspired from the Aspect Oriented Programming (AOP) paradigm which was initially conceived to support the separation of concerns during the development of monolithic systems. BIP has a formal operational semantics and makes a clear separation between architecture and behavior to allow for compositional and incremental design and analysis of systems. We thus distinguish local from global aspects. Local aspects model concerns at the component level and are used to refine the behavior of components. Global aspects model concerns at the architecture level, and hence refine communications (synchronization and data transfer) between components. We formalize global aspects as well as their integration into a BIP system through rigorous transformation primitives and overview local aspects. We present ${\texttt {AOP-BIP}}$, a tool for Aspect-Oriented Programming of BIP systems, and demonstrate its use to modularize logging, security, and fault-tolerance in a network protocol.

A Proofs

We first prove that the global joinpoints can be selected syntactically (Proposition 1), and then prove the correctness of advice application(Proposition 2).

Proof

(Proof of Proposition 1 ). We consider a global event $\left\langle q, a, q' \right\rangle \in \mathcal{E}$ and a global pointcut expression $\left\langle p, v_r, v_w \right\rangle$. The proof follows from the definition of $\mathrm {match_{g}}(\mathcal {C}, gpc)$ which selects all interactions matching the criteria that should be matched by $(E_i = \left\langle q , a, q ' \right\rangle \vDash gpc )$.

Proof

(Proof of Proposition 2 ). We assume that $f_b$ and $f_a$ can be uniquely determined and are not empty. It is possible to add an assignment statement at the start and end of each $f_b$ and $f_a$ which has no effect and is not present in the original system and acts as a marker (example: $x = x + NUM - NUM$, with NUM being a unique number not found in any other assignment). We consider an event $\left\langle q_s, a, q_e \right\rangle \in \mathcal{E}'$, and $\mathrm {rem}_\mathrm {g}(\left\langle q_s,a,q_e \right\rangle ) = \left\langle q'_s, a', q'_e \right\rangle$ the constructed event without the advice.

An event interaction’s update function a.func starts with $f_b$ and ends with $f_a$, according to the definition of $\mathrm {m}()$ in Definition 18 iff it is the result of weaving the advice on it from an interaction $a'$ ($\exists a' \in \gamma : \mathrm {m}(a') = a \wedge a' \in \mathcal {I}$). The interaction $a'$ is in $\mathcal {I}$ iff it was selected by the local pointcut expression ($a' \in \mathrm {match_{g}}(\mathcal {C}, gpc )$). According to Proposition 1, any event with interaction $a' \in \mathrm {match_{g}}(\mathcal {C}, gpc )$ is a joinpoint, specifically $\left\langle q'_s, a',q'_e \right\rangle = \mathrm {rem}_\mathrm {g}(\left\langle q_s, a, q_e \right\rangle )$.