3. Making sense of the terminology soup
Architectural Styles
Architectural Patterns
Design Patterns Architecture
Design
Code/Detailed Design
4. SOA vs. REST
Distributed Pipes and Layered Client Replicated Uniform Virtual
Agents Filters System Server Repository Interface Machine
Stateless Code On
Cacheable
Comm. Demand
SOA REST
5. REST = "Representation State Transfer"
Categorization
App
Categorization
(Resource)
Data
Management
(Resource)
6. Layers should have some constraints
on communications
Layer?
Layer?
Layer?
Layer?
7. Layers should have some constraints
on communications
Layer
layer
Component
Layer
Component
8. Layers should have some constraints
on communications
Layer
Component
Layer
Component
Layer
9. Client/Server
Client Server
Request
Capabilities (services)
Requests initiator
Reply
10. Replicated
Repository is copy copy copy
about having
copy copy copy
more than one
copy providing copy copy copy
the same
service looks like one copy
better performance and latency
15. http://devrig:52141/RM/Sessions/abc/
• ATOMPUB
– Session details
• URI (ID)
• State (start/end/status etc.)
• Resources
– Knows status
– URI for the Resource representation on the RM
– URI for the Resource itself
I am not going to talk about the “Code On Demand” since it is optional (also easy to understand – think javascript)
RR is the precursor for cacheability (!)
trades-off efficiency of interaction for easier of integration and better independent evolvability of resources
In a nutshell document-centric means that the message contains enough information to represent a complete unit of work. RPC calls tend to be geared toward sending just the parameters needed to perform the action and have some stateful expectations from the service. Document-centric message, on the other hand, don’t make these assumptions, having a complete unit-of-work, means that the service has enough information or context in the message to understand all the state it needs. This also means that document centric messages are usually more coarse grained compared with their RPC counterparts. Table 5.2 below demonstrates 3 ways document centric messages can contain more context. ContextExplanationHistoryThe message can contain the interaction up to this point - sort of like breadcrumbs in ht Hansel and Gretel tale. For instance in an Ordering scenario, if the first step was to get customer data and the current step is to set the order (each step can be with another service) the message would contain the customer information when it goes into the ordering service.Future The message can include the options the consumer can take to complete the interaction. Again, if we think about an ordering scenario, if the previous step was to reserve the order (see Reservation pattern in chapter 6), the return message can include the information needed to confirm the reservation.Complete Future Another way to provide context is for the message format to contain the complete details needed for the interaction. For the ordering example, this would mean that the message would have a skeleton to support all the order and related details and the parties involved will fill in the blanks as the interaction progresses.
(contrast this to objects that encapsulate them)
where you can actually find the thingor rather Representations of ite.g.in this case (www.uri.com.hk) representations of underwear fashion
HTTP defined a protocol (headers, verbs + response type etc.)GETPUTPOSTDELETEOPTIONSHEAD(TRACE –loop back the request as it is received by the server, can be a security hazard) CONNECT – defined in the spec as reserved)
e.g. Waka by Roy Fielding with things likeRender ~ GetMonitor – subscribe to changes
In UPDATE you can send only the “diff” using put (and the document centric messaging) you can only replace
Can be used to check if state changed since last time if retrieving the body is a heavy operation
e.g. when you call the root URI it will let you know
Easier integration It isn’t that integration magically happen because of the uniform interface – but it is easier for humans to understandIn RESTful HTTP integration is even easier because HTTP is ubiquitous so it is also easy to integrate cross-platformEasy to expose services to UI esp. in the technologies we choseaNot without challenges e.g. – getting security right, getting URIs right
We already seen that
As mentioned REST trades-off efficiency for interoperability and integrationWhen you do need efficiency then REST is wrongIt was also designed for Hypermedia systems (i.e. Web) if your solutions can’t support that, than it is wrong.If you have to integrate existing stuff that is not RESTful than it is wrongEtc.
A lot of people don’t understand REST and can create havoc just like in RPC based systeme.g. translating every verb into a URI:http://www.example.com/DoActionThe fallacies of distributed computing still matter REST does encourage some of the recommended practices (e.g. statelessness of communications, document centric messages, use of cache etc.)
It builds on simple concepts But you should be mindful to get it rightDefine the correct ResourcesUse cache (e.g. ETAG and Last-Modified in HTTP) Parse data in and out etc