REST CS 4720 Mobile Application Development CS 4720 And verily - - PowerPoint PPT Presentation

CS 4720

REST

CS 4720 – Mobile Application Development

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 J… 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?

CS 4720

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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Describing the World

• We generally refer to client/server systems as

“two-tier systems”

• Why?
• What does that communicate?

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A Three-Tier System

• How might a three-tier

system be different than a two tier?

• Do we add a server?
• Do we add a client?
• What does it mean to have

three tiers?

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Context Clues

• It’s all in what you’re talking about.
• If you’re discussion the
• verall system, including

the client, a common view of a three-tier architecture might be this:

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Principles of REST

• Remember this one?

– 3. Addressable Resources – Everything has its place and every place has a thing – “Everything is a resource”

• This is actually key to how we go about

building a three-tier web application

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RESTful Tiers

• If every resource is a place, and every place is a

resource, how do we define our resources?

• We know the URL would look something like:

– http://mysite.com/users/mss2x

• Where:

– mysite.com is the domain – users is the “category of resources” – mss2x is a specific instance of the resource

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RESTful Tiers

• What we want the web server / web

application to do is translate this:

– http://mysite.com/users/mss2x

• Into effectively a function call that

– Identifies what the user is asking for – Loads a particular resource – Displays the pertinent info about that resource back to the user

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Model-View-Controller

• This is the definition of what MVC is
• The MVC pattern maps:

– Identifies what the user is asking for – Loads a particular resource – Displays the pertinent info about that resource back to the user

• To Model, Controller, View (in that order)

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MVC

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MVC

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REST and MVC

• REST and MVC aren’t directly related, but they

intersect in many, many ways

• The idea of “nouns” in the system – of

addressable resources – is a major component

• f both
• In general, a good MVC system will be RESTful,

although a RESTful system does not have to follow MVC.