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Web caching and Content Distribution Networks (CDNs) seek to reduce retrieval latency, lower bandwidth usage and reduce load on the origin servers by moving the o ered content closer to the end users. Historically, the content replicated to the edges of the network in this way has been mostly static, such as images. As more dynamic and personalized content is being o ered on the Web, there is a growing need for mechanisms capable of caching and replicating content that changes frequently and is user-speci c. In addition, existing caches heuristically estimate object freshness lifetimes, which results in unnecessary validation traÆc between caches and origin servers, and does not prevent caches from serving stale objects to their clients. In this work we describe a mechanism that makes caching of Web objects more deterministic, reduces validation traÆc, increases the amount of content that may be cached, and reduces the amount of dynamic content that must be retrieved from the origin server. Our mechanism uses a number of techniques in concert. First, objects that constitute a page are classi ed based on their change characteristics. Next, servers analyze relationships between objects in conjunction with object change characteristics and compile them into Content Control Commands. Caches and servers then use these commands to manage objects. Finally, caching and CDN servers construct frequently changing, personalized, or any other pages from individual components using a powerful Content Assembly technique.