The Architecture of the World Wide Web

1. Architectural Basis of the Web
 : The notion of a resource is central to the architecture of the Web
 - We need to be able to identify resources, represent resources and interact with resources

2. Identification
 1) Identifiers should be global: Global naming leads to global network effects
 2) Every object should be addressable
 3) Uniform Resource Identifiers (URI): A compact string of characters for identifying an abstract or physical resource
  <scheme>:<hierarchical part>?<query>#<fragment>
  e.g. http://www.example.org/aboutus?name=a#staff
 4) Assign distinct URIs to distinct resources: Using the same URI to directly different resources produces a URI Collision
 5) Avoid URI aliases: A URI owner should not associate arbitrarily different URIs with the same resource

 6) The Classical View: Early to mid-90s web specs distinguished between
  - Resource Location (URL): URL resolution is (usually) well-defined
  - Resource Name (URN): URNs don't necessarily have well-defined resolution semantics
  - Resource Identifier (URI)
  => URI ⊃ URL + URN

 7) The Modern View: Formal URL/URN distinction is unhelpful
  - URL is a useful informal concept

3. Representation
 1) Representations of a resource may be sent or received using interaction protocols
 2) Separation of content, presentation and interaction: A specification should allow authors to separate content from both presentation and interaction concerns
 3) Link identification: A specification should provide ways to identify links to other resources, including to secondary resources
 4) Web linking: A specification should allow Web-wide linking, not just internal document linking
 5) Generic URIs: A specification should allow content authors to use URIs without constraining them to a limited set of URI schemes
 6) Hypertext links: A data format should incorporate hypertext links if hypertext is the expected user interface paradigm

4. Interaction
 1) Dereferencing URIs: The schemas in URIs used to identify resource may indicate protocols that can be used to access those resources
 2) Reuse representation formats: New protocols created for the Web should transmit representation as octet streams typed by Internet media types
 3) Safe retrieval: Agents do not incur obligations by retrieving a representation
 4) Available representation: A URI owner should provide representations of the resource it identifies
 5) Reference does not imply dereference: An application developer or specification author should not require networked retrieval of representations each time they are referenced
 6) Consistent representation: A URI owner should provide representations of the identified resource consistently and predictably

https://www.w3.org/TR/webarch/