ing computation and work as modifications to the representation. It’s REST
or changes to the representation that
Every verb (operation) can be
nouned (cast as data).
These nouns are described as URLs.
Operations are cast into identities
represented at URLs.
Identity is RESTing on its laurels. The
identity captured in the URL is a large
part of why REST is so powerful. The
underlying resource has an identity in
the URL namespace. Each representation (assigned to a single user) has an
identity in the URL namespace. Specific operations are captured, leveraging
identity within the URL namespace—a
powerful mechanism using the identity of the URL!
Identities must be scoped in space and
time so they do not cause ambigui-ties. This is, on the one hand, an obvious and silly thing to say. On the other
hand, it is a liberating concept.
Identifiers may have permanent
unique IDs like those offered by UUIDs.
These are powerful and useful. Identifiers may have a centralized or hierarchical authority that assigns their IDs, and
that, by itself, offers challenges: Does
this authority scale? Is it broad enough
in its role to encompass the many different pieces of the solution?
The reality for most systems is that
identities span the participants that
see the use of that specific identifier.
When merchants interact with a big
e-commerce site, they will have shared
identifiers for their cooperative work.
Still, the merchants may not share the
identifiers they use to deal with
private suppliers. Those private suppliers
may have different identifiers used
to interact with the manufacturers of
The scope of the identifiers is typically subject to the portion of the workflow that hosts the identifier. There are
global IDs like UPC or SSN (Social Security number), but there are also local
IDs like SKUs that are defined only for
a single merchant.
The ‘I’s Have It
Identity is an extremely important
part of our systems. Its real power is
unleashed when combined with three
tional state transfer3 (REST) is an in-
teresting and influential pattern that
leverages HTTP and URLs. In the REST
pattern, resources are implemented as
client-server calls, which are stateless.
Stateless means each request from the
client holds enough information to
process the request at the server with-
out taking advantage of any context
stored at the server. The session state is
effectively held at the client.
Resources and representations.
Within REST, resources are any piece of information that can be named. Typically, the name of a resource is a URL.
resource is frequently used to represent
groupings of related stuff that may be
used to do work. The contents of a resource may be static or dynamic. What
is essential is that it can be named.
REST resources may project one or
more representations. Each representation is a view onto the resource that
may or may not be customized for each
user. The resource is itself given its
own URL(s) as identities.
RES T: Representational state transfer.
Users wishing to work with the resource
are given their own representations as
identified with one or more URLs. The
resource may have many users. The
vast URL identity space is subdivided
into representations for each user. Requests for work are accomplished with
HTTP PUT commands making modifications to the representation.
Scribbling on the representation.
Changing the state projected in the
representation is how work is done.
The combination of the representation
(possibly personalized to the client)
and the ability to scribble changes on
the representation allows many clients
to work with the resource.
URL: Mixing identity, operations, and
session state. As changes to the representation occur, responses to the
HTTP PUT requests are wrapped up in
the URL returned. Contained in that
URL is the session state describing
ongoing and potentially long-running
work for this client.
Identity in the URL captures the op-
eration to be performed.
Identity in the URL captures the ses-
sion state of the work!
REST: Every verb can be nouned.
REST maps a user’s perspective to a set
of URLs for the representation. REST
also defines the mechanism for invok-
The real art of
lies in finding
a way to identify
set of individuals.