The web in a few minutes

Every FHIR call is a web request

FHIR's main way of exchanging data is the web. So before the FHIR calls make sense, it helps to know three things: what an address is made of, what a request is, and what comes back. This takes a few minutes.

A URL has named parts

An address on the web is a U R I, often called a U R L. The standard breaks one down into parts. The scheme comes first, before the colon: here, https. Then the authority: the host name, which may be followed by a colon and a port number. Then the path. Then, after a question mark, an optional query. And after a hash, an optional fragment. The standard's own example address has all five; the port number is left out here to keep it short.

• https://example.com/over/there
• ?name=ferret#nose

A client asks. A server answers.

Almost everything on the web is one pattern: a client sends a request, and a server sends a response. H T T P, the protocol, is described in its standard as a family of stateless, application level request and response protocols. Stateless means each request can be understood on its own, without the server remembering earlier ones.

• A browser
• An app
• A script
• Receives requests · gear
• Sends responses · share

Ask for a record, get a record

Here is a real exchange. The request, on the left, asks for one resource: get, the path Patient slash one two three. The server, on the right, replies with a status line, two hundred O K, a header saying the content is JSON, and then the content itself: a small made up patient record. The first line of a request says what to do and where. The first line of a response says how it went.

• GET /Patient/123 HTTP/1.1
• Host: localhost
• Accept: application/json

Check yourself

Pause and think. What does the scheme part of a U R L, such as https, tell you? The answer: which protocol to use to reach the resource.

• Which protocol to use to reach the resource
• Which file the resource is saved in
• Which person owns the server
• How big the answer will be

Keep these in mind

A U R L has a scheme, an authority, a path, a query and a fragment. A client sends a request, and a server sends a response. H T T P is stateless, so each request stands alone. And the first line says what to do, or how it went.

• A URL has a scheme, an authority, a path, a query and a fragment
• A client sends a request; a server sends a response
• HTTP is stateless: each request stands alone
• The first line says what to do, or how it went