1. Enterprise Service Bus
Customized company message broker
Arriving SOA requests
Using TCP/IP, SOAP, JMS, FTP etc. protocol
Wrapped by ESB layer
To provide web based inputs to an organisations legacy business process orchestration technology
Something of a “buzz” word
Spring 2017
(c) Ian Davis

2. Asynchronous Messaging
Peer-to-Peer
Peers talk to other Peers one at a time
May expect synchronous or asynchronous response
Asynchronous handled by a callback (new thread)
Publish-Subscribe (one to many messaging)
Provider communicates with Topics
Subscribers dynamically subscribe to Topics
(Implicit Invocation / Observer design Pattern)
Topics may be organised hierarchically
Topics forward messages to subtopics/servers
Spring 2017
(c) Ian Davis

3. Application Servers Client/Browser Side (Not part of server)
HTML, Javascript, Ajax
Web Tier (e.g. Apache, Tomcat)
Receives requests
Invokes web server-hosted components
JSP (Java Server Pages), ASP, PHP, etc.
Invokes business component tier
JavaBeans, .NET, CORBA
Invokes Enterprise Information Systems Tier
MySQL, Backend Mainframe, etc
Spring 2017
(c) Ian Davis

4. Enterprise JavaBeans (EJB)
Top layer is a Java Virtual Machine
This hosts components
Session Beans (Synchronous)
Stateless (consecutive requests to any instance)
Stateful (caller binds to one specific instance for life)
Message-driven Beans (Asynchronous)
No explicit reply
Spring 2017
(c) Ian Davis

5. Mobile Architecture
Spring 2017
(c) Ian Davis

6. Examples Software downloaded before execution
Java Applets download jar when used
Javascript embedded in transmitted HTML
Viruses (e.g. Liquid and Hadoop)
Hadoop
Move the code to where it is needed
Move the code to become local to the data
Not massive amounts of data to remote code
Spring 2017
(c) Ian Davis

7. Message Oriented Choices
Delivery: Best effort, Persistent, Transactional
UDP , TCP/IP, Message Queues
Blocking / Non-Blocking / Asynchronous Sockets
Blocking good for simple connection (layered)
Non-Blocking more flexible since no waiting (layered)
Eg: Cancel attempt to connect, switch to different web page
Asynchronous efficient/elegant/scales well (event driven)
Keep track of connection state – not every connection
Interface: Sockets, RPC, HTTP, SOA, Ajax, Stream
Spring 2017
(c) Ian Davis

8. Representational State Transfer (ReST)
URL + Parameters returns Document
Leverages Standard Web Technology
GET/POST/PUT Built on top of
Stateless
Except for Cookies and/or Session
Server indicates cacheability
AJAX
Small document transfers while viewing
Spring 2017
(c) Ian Davis

9. Roy Fielding on his 2000 PhD thesis
Throughout the HTTP standardization process, I was called on to defend the design choices of the Web. That is an extremely difficult thing to do within a process that accepts proposals from anyone on a topic that was rapidly becoming the center of an entire industry. I had comments from well over 500 developers, many of whom were distinguished engineers with decades of experience, and I had to explain everything from the most abstract notions of Web interaction to the finest details of HTTP syntax. That process honed my model down to a core set of principles, properties, and constraints that are now called REST
Roy Fielding on his 2000 PhD thesis
Spring 2017
(c) Ian Davis

10. RESTful Web Services
Web services only uses HTTP as a transport layer (to fool firewalls)
Representational State Transfer (REST)
Resources identified by a URL
Message passing mechanism
GET (Parameters follow URL)
POST (Parameters body of HTTP message)
PUT (Upload to a named URL)
DELETE (Delete now/later something at named URL)
Spring 2017
(c) Ian Davis

11. ReST Constraints Client/Server → Parallel evolution (Adaptable)
Stateless → Scalable
Cacheable → Efficient
Layered → Transparency
Mobile Apps → Powerful
Uniform Interface → Usable
Wikipedia
Spring 2017
(c) Ian Davis

12. Uniform Interface Identification of all universal resources
Naming of things (conceptual separation)
URL / URI
Manipulation of resources
Client read, change or delete a named resource
Self descriptive messages
Nothing is assumed by the server (Extensible)
Hypermedia (Resources explain themselves)
Circumvents Firewalls by using HTTP port
Spring 2017
(c) Ian Davis

13. Get versus Post GET → Retrieve Parameterized URL
Visible so bad for sensitive data
Can be changed which is bad for security
Can be cached, bookmarked, in history
Length restrictions on parameterization
POST → Send data to the server in
Hidden so better for sensitive data (but not safe)
Can’t be cached, bookmarked or remembered
No length restrictions
Spring 2017
(c) Ian Davis

14. Semantic Web Effort to give XML entities real semantics
Namespaces disambiguate entity names
XMLSchema types the contents of an entity
RDF describes semantic information as graph
Resource Description Framework
RDFS uses RDF to describe objects
OWL defines ontological relationships (isa/hasa)
SPARQL permits queries about semantics
Spring 2017
(c) Ian Davis

15. Service-oriented Architecture (Web Services)
Fix interoperability problems
Vendors agree on standards for application integration
This provides interoperability across hardware, software, companies and infrastructures
Provide internet-scale distributed systems
Vendors agree on standards for distributed computing
Spring 2017
(c) Ian Davis

16. SOA design considerations
Boundaries are explicit
Crossing process, machine, trust expensive
Services are autonomous
Can change code, language, machine transparently
But must preserve backwards compatibility
Services simply receive messages and reply
Not objects, no interfaces, inheritance etc.
Client/server policy part of connecting design
Things like message reliability, security, encodings
Spring 2017
(c) Ian Davis