CS 4720

RESTfulness

CS 4720 – Web & Mobile Systems

CS 4720

And verily the Intarwebz were created• The evolution of the web

– Server / Client– Simple pages– Web applications

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And verily the Intarwebz were created

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And verily the Intarwebz were created

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And verily the Intarwebz were created

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The Statefulness… or lack there of…• How does state play into SIS?• Why? How?

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Nouns speak louder than… verbs…• Look at the links in SIS• What are they? Verbs.• This is the “evolution” of the web

– We have tried to force the web into the same mold as stand-alone programs

– This is not good! – We need to take advantage of the asynchronous

nature of web communication!

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REST• Definition: REST

– Representation State Transfer – a software architectural style for distributed

hypermedia systems, such as the web– (but not necessarily the web)

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Principles of REST• 1. Statelessness• In the simplest terms, this principle forbids for

any state information to be stored on the server

• This does not forbid state to be stored client-side

• Every message though must contain all information needed for understanding

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Principles of REST• 2. Idempotency • The output of identical requests is itself

identical• In other words, if you go to the same page

twice, you get the same page (barring changes in the content model)

• Allows for caching, which improves user-perceived responsiveness

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Principles of REST• 3. Addressable Resources• Everything has its place and every place has a

thing• “Everything is a resource”• See amazon.com for a good example• URLs reflect the resource

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Principles of REST• 4. Well-defined operations• In the context of the Web and HTTP, we’re

talking:– POST– GET– PUT– DELETE

• This reflects possible actions

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Principles of REST• 5. Formatted/Structured Data• The resources you get should be encoded in a

uniform way (like HTML, XML, etc.)

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Sounds good… but…• Sure sounds hard to pull off good web apps

with these constraints…• Let’s think about a shopping application• What’s the “usual” way?

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RESTful Shopping• What are the actions that you want to take in a

shopping application?

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RESTful Shopping• In real life, who holds the shopping cart? • You, or your personal shopping buddy provided

by the store?• If it’s you (and I hope it is) where do you store

cart information?– In a frame? (UGH… I just threw up a little in my

mouth)– In a cookie? (not what it’s meant for!)– HTML5 SessionStorage object … eventually

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RESTful Shopping• Well, just for argument, we’ll give you your

shopping buddy (we’ll call him “Carl”)• In this instance, the shopper will be asking the

store to set aside items for them• The difference here is basically philosophical,

but bear with me• If we treat the cart as part of the STORE and

not owned by the CLIENT, then RESTfulness can still be maintained

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RESTful Shopping

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Sender Message

Client Show me your products.

Server Here’s a list of products.

Client Okay, I’d like to buy 2 of http://shop.com/product/X, place it in my basket, my username is “XtremeShopper” and password is “bubba”

Server Done. I’ve put it in your basket at http://shop.com/users/XtremeShopper/basket

Client Actually, I don’t need 1 of those. Please remove one of X from my basket, my username is “XtremeShopper” and password is “bubba”

Server Done. I’ve removed it from your basket at http://shop.com/users/XtremeShopper/basket

Client Great. Ring it up - username is “XtremeShopper” password is “bubba”

Server Should I charge that to your account?

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RESTful Shopping• Uh… wasn’t that a session?• Not quite – a session disappears when the user

does– Theoretically, this would be around until the user

removes everything or checks out• It is addressable, it’s formatted, it’s

idempotent, and it uses defined operations• The differences are very subtle, but they are

there

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Sounds good… but…• REST means that the server is stateless and

cannot store any data about the client’s current state/session

• This example was a bit extreme• Like most things, moderation is the key to

getting the right balance between server and client resource utilization

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Your turn• Let’s go find some RESTful and non-RESTful

apps. • Why are they behaving that way?• Why do you think they were designed this

way?

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Review REST• REST: Representational State Transfer• It is a software architecture style / philosophy,

not a protocol / system / etc.• Main Principles:

• Stateless client-server – No state info is stored server-side

• Identification of resources - Individual resources are identified in requests, for example using URIs

• Manipulation of resources through a simplified set of operations – In HTTP, POST, GET, PUT, and DELETE

• The use of structured data – Such as HTML or XML

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REST Examples• What web systems are RESTful? Others?

– CS4720 homepage? Yes.– cnn.com? Potentially.– Collab? The architecture potentially, but not the

individual modules.– SIS? Is there a rule it doesn’t break?

• Remember the fundamental concept: nouns (resources), not verbs (actions) to interact

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