Formalizing Visibility Characteristics in Hierarchical Systems
Abstract
We consider hierarchical systems where nodes represent entities and edges represent binary relationships among them. An example is a hierarchical composition of Web services where the nodes denote services and edges represent the parent-child relationship of a service invoking another service. A fundamental issue to address in such systems is, for two nodes X and Y in the hierarchy whether X can see Y , that is, whether X has visibility over Y . In a general setting, X seeing Y may depend on (i) X wishing to see Y , (ii) Y wishing to be seen by X, and (iii) other nodes not objecting to X seeing Y . The visibility could be with respect to certain attributes like operational details, execution logs, security related issues, etc. In this paper, we develop a generic conceptual model to express visibility. We study two complementary notions: sphere of visibility of a node X that includes all the nodes in the hierarchy that X can see; and sphere of noticeability of X that includes all the nodes that can see X. We also identify dual properties, coherence and correlation, that relate the visibility and noticeability notions, and study their variants.
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