Technology Jornal: Punit Kaishap

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JMS Concepts

JMS is an API that allows applications to create, send and receive messages

Two main properties of JMS:

Asynchronous: A JMS Provider can deliver the message once a client is available
Reliable: Ensures delivery once and only once

JMS Provider:
It is the messaging system that implements the JMS interfaces and provides administrative and control features

Point to Point Messaging:
When to use: Use PTP when every message you send must be processed successfully by one consumer.

Steps:

Message is sent to a Queue
Receiver picks up the message
Message is retained until it is picked up by JMS Client

Publish / Subscribe:
When to use: Use Pub / Sub when there are multiple consumers for the same message

Steps:

Message is sent to a Topic
Subscribers of that Topic are notified
Subscribers pick up Message from Topic

Note: Publishers and Subscribers are generally anonymous

ConnectionFactory:
Client uses the ConnectionFactory to create the connection with the provider (e.g. QueueConnectionFactory / TopicConnectionFactory)

Session:

The Session object is used to create the Queue Sender and Queue Receiver
The Session object can be used to create an asynchronous message listener
The Session object can be used to commit or roll back the transaction

Sample code:
queueConnection.createQueueSession([boolean to indicate transacted session],[integer to indicate Acknowledgement Mode])

Transacted Session values
- Transacted Session on: True
- Transacted Session off: False
Acknowledgement modes:
- AUTO_ACKNOWLEDGE
- CLIENT ...
- PUB_SUB ...

Durable subscription:
The Durable subscriber program shows how durable subscriptions work. It demonstrates that a durable subscription is active even when the subscriber is not active.

Destination:
Refers to the location where a message is created
Refers to the location where a message is to be sent

Message Driven Beans (MDB):
The MDB allows J2EE applications process JMS messages asynchronously. Session and Entity Beans allow you to send messages synchronously.
The EJB Container - notes:

Creates the message consumer (QueueReceiver or TopicSubscriber)
At deployment time the MDB is associated with a destination and to type of subscription (these entries are made in the Deployment Descriptor
No need to call setMessageListener
Implement the class javax.ejb.MessageDrivenBean

Steps to use MDBs:

Create the Message Consumer
Register the Message Listener
Specify the Message Acknowledgement Mode

Java Concepts

Multiple Inheritance:
Java does allow for multiple inheritance. One may extend a SuperClass and implement multiple interfaces. However, it is not the concrete multiple inheritance as available in C++. In Java concrete multiple inheritance can be achieved by Composition & Delegation

Example implementation:

interface A() {
public void aMethod();
}

interface B() {
public void bMethod();
}

class AHelper implements A {
public void aMethod() {
  // some implementation
}
}

class BHelper implements B {
public void bMethod() {
  // some implementation
}
}

class Alphabet implements A, B {
public void a() {
  AHelper aobj = new AHelper();
  aobj.a(); // Delegation
}

public void b() {
  BHelper bobj = new BHelper();
  bobj.b(); // Delegation
}
}

Advantages of this approach:

Achieve multiple inheritance
Flexibility of changing the implementation of aMethod() and bMethod() in one place

Web Service Concepts

WSDL: Web Service Definition Language
It is an independent communication protocol or data format. It supports the following protocols:

Protocol	Synchronity	Data Format	Description
HTTP	Sync & Async	GetPost, XML & SOAP	Unsecure, platform independent, remote
HTTPS	Sync & Async	GetPost, XML & SOAP	Secure, platform independent, remote
JMS	Async	XML, java objects & SOAP	Peer to peer communication & Publish / Subscribe
SMTP	Async	Context based, XML, & SOAP	Remote ...
CORBA	Sync	Corba Object	Direct remote object invocation

Finance Concepts

Option:
The right buy not the obligation to buy (call option) or sell (put option) a specific amount of a given stock / commodity / index at a specified price (strike price) during a specified period of time.

Prime Broker:
Acts as a settlement agent, provides financing for leverage, custody of assets for money managers, hedge funds, professional investors, etc.

Broker / Dealer:
Any individual or firm in the business of buying and selling securities for itselt and others. B/Ds must register with the SEC.
Broker, executes orders on behalf of his client
Dealer, executes trades on behalf of his firm

Financial Leverage:
The degree to which an investor is utilizing borrowed money.

Asset Class:
Type of investment - stocks, bonds, real estate or cash

Derivative:
A financial instrument whose characteristics and value depend on an underlying bond, equity, currency or commodity. Examples are Futures and Options
Future: A contract for delivery of product at a price on a future date
Option: No obligation to buy the financial instrument

Rule Engine Concepts

Different types of rules:

Declarative rules: set of rules that compute values or enforce constraints
Decision tree rules: rules that use forward chaining to make a decision
Process rules: rules to manage the receiving, assignment, routing and tracking of work

Forward chaining:
Forward chaining is defined as a data driven technique used in constructing goals or reaching inferences derived from a set of facts, example implementation: JESS - Java Expert System Shell (http://herzberg.ca.sandia.gov/)

Backward chaining:
Backward chaining starts with the desired goal and then attempts to find evidence to prove that goal

Current Rule Engine framework can be defined in 4 layers:
1st Layer: Operating System
2nd Layer: Database
3rd Layer: Rules
4th Layer: Applications

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