HTTP transactions have semantics that can be interpreted in many ways. At a low level, a physical stream of bits is transmitted from server to client. Higher up, those bits resolve into a message with a specific bit pattern. More abstractly, information, regardless of the physical representation, has been transferred. While the mechanisms associated with these abstractions, such as content negotiation, are well established, the semantics behind these abstractions are not. We extend the library science resource model Functional Requirements for Bibliographic Resources (FRBR) with cryptographic message and content digests to create a Functional Requirements for Information Resources (FRIR) ontology that is integrated with the W3C Provenance Ontology (PROV-O) to model HTTP transactions in a way that clarifies the many relationships between a given URL and all representations received from its request. Use of this model provides fine-grained provenance explanations that are complementary to existing explanations of web resources. Furthermore, we provide a formal explanation of the relationship between HTTP URLs and their representations that conforms with the existing World Wide Web architecture. This establishes the semiotic relationships between different information abstractions, their symbols, and the things they represent.