sca assembly extensions for event processing and pub/sub€¦ · what is event processing and...

SCA Assembly Extensions for Event Processing and Pub/Sub

Specification Location

http://osoa.org/download/attachments/35/SCA_Assembly_

Extensions_for_Event_Processing_and_PubSub_V1_0.pd

f?version=1

Delta on SCA Assembly Model Specification 1.0

http://osoa.org/download/attachments/35/SCA_Assembly_Extensions_for_Event_Processing_and_PubSub_V1_0.pdf?version=1




Outline

What ?

Why ?

Motivation

Use cases

Comparison with the service-reference model

Why the service-reference model isn’t sufficient

Overview of the SCA Event Processing spec

Examples

Details

Event processing in Java-based component

What is Event Processing and

Pub/Sub

Event processing consists of computing/performing

operations on events or event messages

Creating, reading, transforming event objects/representations

Components interact via events

Pub/sub is a style of organizing components

Components produce and consume events

Producers and consumers are decoupled from each other

NxM

Dynamic

Consumers specify subscriptions (may contain filters)

Blind Men and Pub/Sub

Why ?

Very common and well accepted model

Decoupling of producers and consumers

Pull vs. push

Integration with existing infrastructure and

computing/interaction models

Application integration involving composite applications

require it

Components may interact in a mixed model (service

invocation and pub/sub)

Events don’t impose any operational semantics

launchMissile() vs. [WMD found]

Scenario 1 – Sales Event

Processing Phase 1

Phase 1 focuses on order processing flow

Phase 1 is successfully deployed to production

Because order processing is at the core of the company business:

any modification to this flow has to go through long and stringent testing.

Performance is paramount –no new service can be introduced if it implies a degradation of the customer experience.

Scenario 1 – Phase 2

After a few months,

Marketing decides to

introduce a new real-time

business intelligence

tool.

Just needs to “tap” into

existing events

Non-intrusive: No need

to modify/version/re-test

core order capture

process (with associated

costs savings)

Addition of new services

has no performance

impact on core order

capture process

(repeat with Fraud

Detection, and again,

and again)

Scenario 2 – New Employee Provisioning

Scenario 3: Complex Event

Processing Application

Real time responses required

Multiple event streams processed by multiple consumers

E.g.: Multi-player gaming systems, algorithmic trading

applications

Invocations vs. Events

Invocations

A client component wired to a service component invokes operations

on the service.

The operation has some implied semantics – there’s an expectation

that something specific will happen.

Operations of related semantics typically grouped together –

component expected to process any operation request

There may be a response directly back to the client

Invocations vs. Events (2)

Events

Not directed at any single component

Maybe received by more than one component

No implied semantics – each receiving component may react very

differently

No way to respond directly to the producer

A component doesn’t have to receive all events from the same source

Decoupling of “interfaces” between producers and consumers

Consumers can set filters

Can Service-Reference model be

used for Event Processing?

Service => consumer

Reference => producer

Reference cardinality is 0..n

Autowire

Can Service-Reference model be

used for Event Processing?

Impedance mismatch => no maximum power transfer

Different model / way of thinking: wires not included

No decoupling

Requires interfaces for typing

Interface/operations have processing semantics, events don’t

Doesn’t allow addition of producers/consumers dynamically

No ability to set filters

Various issues crop up because of the model mismatch. For

example, sca:reference (0..n) is mapped to an array in Java

Subscribers do not offer services they offer callbacks

Services do not subscribe they make software functionality

available for others to use.

A subscribe message will be sent from a service to a

reference: a direction reversal

Changes are hard to manage

Overview

New concepts:

Events

Event types

Event Description Language (EDL)

Producers

Consumers

Channels

Filters

Diagram

Component

services

producer

properties

Implementation

- Java

- BPEL

- Composite

…

references

consumer

Events

Message sent to zero or more parties that contains

information about a situation that has occurred

Events must have one or both of:

a type, to identify the situation (a QName)

Sometimes a type isn’t required or wasn’t present when

the event was generated

a body containing details of the situation

Sometimes a body is not required, just knowing the type

is good enough

Canonical representation is XML

Event Type

An event can have an associated event type

Is identified by a unique QName

Can have an associated body type or shape and

constraints on the event

A body type/shape may be used for multiple event types

Body type are defined in an existing type system like XML

Schema or Java

EDL

Simple Event Type Definition Language (EDL) to express

association of event types and body types

Extensible

<sca:eventDefinitions targetNamespace="anyURI">

<sca:eventType name="NCName"? >*

...

</sca:eventType>

</eventDefinitions>

EDL (2)

Can use XML Schema

<sca:eventDefinitions targetNamespace="anyURI">

<sca:eventType.xsd name="NCName"? element="Qname" />*

</eventDefinitions>

<eventDefinitions

xmlns="http://www.osoa.org/xmlns/sca/1.0"

xmlns:foo="http://foo.com"

targetNamespace="http://foo.com">

...

<sca:eventType.xsd name=“EarthQuakeType”

element="foo:EarthQuake"/>

</eventDefinitions>

Producer

Entity that creates events

Implementations/ComponentType can declare producers

Are configured by specifying the target

Can be promoted to produce composite producers

Can be configured to send events to multiple destinations

Consumer

Entity that receive events

Implementations/ComponentType can declare consumers

Are configured by specifying the source

Can be promoted to produce composite consumers

Can receive events from multiple destinations

Can specify filters

Channel

Channels connect zero or more producers to zero or more

consumers

A channel may have filters to define what events it will

pass on

A Channel is either a Domain channel or private channel

Domain Channels are visible to all components regardless

of nesting of that component in another component

Private channels are only visible within the component that

defines them

An SCA Domain always has a default channel “//” which

any component can use

if there’s no reason to partition your space you don’t

have to

Filters

Selects a subset of events from a source

Consists of filter expressions of type boolean

Each filter expression is on

event type (sca:NULL is a special value signifying no type)

business data

metadata

Multiple filter expressions are logically ANDed

Filters have no side-effects and no state

Filters specify three things: dialect, subject & expression

QName of the filter => dialect and subject

Filters (2)

<filters>

<type qnames="list of xs:QName"?

namespaces="list of xs:anyURI"? />*

<body.xpath1> xs:string </body.xpath1>*

<metadata.xpath1> xs:string </metadata.xpath1>*

<any/>*

</filters>

Filters (3) -- Examples

<type qnames="ns1:printer ns2:printer" />

<type qnames="sca:NULL" />

<type qnames="sca:NULL ns1:printer" />

<type namespaces="http://example.org/ns1

http://example.org/ns2" />

<type qnames="ns1:printer sca:NULL"

namespaces="http://example.org/ns2" />

Example 1: Connection via Local

Channel (diagram)

Composite X

Component

4

Channel

A

Component

2

Component

3

Component

1

Example 1: Connection via Local

Channel (XML)

<composite ...>

<component name="Component1">

<implementation.java class="..."/>

<producer name="Foo_Events" target="ChannelA"/>

</component>




</component>



<consumer name="Foo_Handling" source="ChannelA"/>

</component>




</component>

<channel name="ChannelA"/>

</composite>

Example 2: Promotion (diagram)

Composite X

Component

2

Component

3

Component

1

Channel

A

Example 2: Promotion (XML)

<composite ...>


<implementation.java class="…"/>

<consumer name="Bar_Handling"/>


</component>



<consumer name="Bar_Handling"/>


</component>

<channel name="ChannelA"/>


<implementation.java class="…"/>


<producer name="Special_Events"/>

</component>

<consumer name="Bar_Handling“

promotes="Component1/BarHandling

Component2/Bar_Handling"/>

<producer name="Special_Events“

promotes="Component3/Special_Events"/>

</composite>

ComponentType Pseudo-schema

<componentType ... >

…

<consumer name="xs:NCName"

requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<filters/>?

<binding/>*

</consumer>

<producer name="xs:NCName"

typeNames="list of xs:QName"?

typeNamespaces="list of xs:anyURI"?



<binding/>*

</producer>

</componentType>

Component Pseudo-schema

<component ... >

...

<consumer name="xs:NCName" source="list of xs:anyURI"?



<filters/>?

<binding/>*

</consumer>

<producer name="xs:NCName" target="list of xs:anyURI"?


typeNamespaces="list of xs:anyURI"?



<binding/>*

</producer>

</component>

Composite Pseudo-schema

<composite ... >

...

<consumer name="xs:NCName"

promotes="list of xs:anyURI"



<filters/>?

<binding />*

</consumer>

<producer name="xs:NCName" promotes="list of xs:anyURI"


policySets="list of xs:QName"?


typeNamespaces="list of xs:anyURI"?>*

<binding />*

</producer>

<channel name="xs:NCName"



<filters/>?

<binding/>*

</channel>

</composite>

Event Processing in Java

Components

Non-normative

New annotations

@Producer

@Consumer

@EventType

What is lacking in the

contribution?

No conformance criteria

RFC 2119 statements to be completed when conformance

defined

Aligned with SCA version 1.0

Specific detailed proposals for C&Is (for other OASIS SCA

TCs)

Bugs (?)

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