Time and order considerations in consistency models for web caching

Consistency is a necessary consideration when dealing with web caching. Although this technique accelerates the web experience for the user, it must provide consistency, i.e., the objects in the cache must be fresh and all the relationships among them must be valid. Both problems have been addressed by several web caching strategies ([4], [5], [7], [9], [12], [18], [23], [25], [26]). However, their formal properties are not completely understood, because practical issues frequently overcome theoretical ones in the web community. In order to offer an environment where formal characteristics can be proved, it is necessary to consider two dimensions in consistency: time and order[2]. These two facets permit an understanding of how fast the changes made in some object are updated in its copies, and what order relationships exist in the events of the system. This paper aims to present both consistency dimensions in order to clarify, analyze and prove, in a formal fashion, properties of web caching consistency models.