2
Implicit Invocation
Indirectly or implicitly calls to methods and interfaces in response to an event or a received message
Publish/Subscribe Event-based
3
Publish/Subscribe
Subscribers register/deregister to receive specific messages or specific content. Publishers broadcast messages to subscribers either synchronously or asynchronously.
4
Pub-Sub LL
Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
5
Event-Based Style
Independent components asynchronously emit and receive events communicated over event buses
Components: Independent, concurrent event generators and/or consumers
Connectors: Event buses (at least one) Data Elements: Events – data sent as a first-class entity over
the event bus Topology: Components communicate with the event buses, not
directly to each other. Variants: Component communication with the event bus may
either be push or pull based. Highly scalable, easy to evolve, effective for highly distributed
applications.
6
Event-based LL
Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
DEB Systems
Typically based on message-oriented middleware (MOM)
Components via implicit invocation Producers and consumers Message interfaces
Message sink Message source
Message Types
Nominal Mapped to statically checkable PL types
Subject-Based “/Weather/Germany/Berlin”
Attribute-Based Key-Value Pairs
Attribute-based Messages
Key-value pairs Key: Name, Value: PicUpdate Key: Sum, Value: 50
Attribute Reading Attribute Adding or Modifying
What Makes It Hard?
Ambiguous Interfaces State-based dependencies
void onMessage(Message msg) { String type = msg.getJMSType();
if (type.equals( “On/Off”) ) { ... } else if (type.equals(“PicRequest”))
{ ... }}
Message
Dispatch
Classifying Message Dependences
Inter-Component Message Dependence
Intra-Component Dependence Control-Flow-Based
Inter-Component Message Dependence
Intra-Component Dependence Control-Flow-Based Data-Flow-Based
Classifying Message Dependences
HW2
Maintenance Tasks Description of changes
Message-based dependencies Why
The applications and MOM platforms Some tools
STOX in general
Monitoring Stock changes and alerting customers Three Important part:
Trigger List Absolute limit:
Triggered if the price of the respective stock is either below or above a specified range
Relative limit: Triggered if the price of a given stock has increased or decreased
a given number of percentages within a given time interval.
Portfolio depicts detailed information about the stocks that a user
currently holds Charts
visualize the price of a certain stock over time
17
KLAX
Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
18KLAX in C2
Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
19
C2 Style
An indirect invocation style in which independent components communicate exclusively through message routing connectors. Strict rules on connections between components and connectors induce layering.
20
C2 Style (cont’d)
Components: Independent, potentially concurrent message generators and/or consumers
Connectors: Message routers that may filter, translate, and broadcast messages of two kinds: notifications and requests.
Data Elements: Messages – data sent as first-class entities over the connectors. Notification messages announce changes of state. Request messages request performance of an action.
Topology: Layers of components and connectors, with a defined “top” and “bottom”, wherein notifications flow downwards and requests upwards.
c2.fw framework
MOM platform that KLAX is built from Enforces C2 Style
Includes C2 components C2 connectors Messages
SPECjms2009
JMS-based MOM TextMessages, ObjectMessages,
StreamMessages or MapMessages Pub/sub (topics) vs. P2P messages (queues)
Performance benchmarks Supply chain of a supermarket company Documentation provided
Unix Commands
find Finds files and directories
xargs Reads from standard input Builds arguments Calls command
grep Regular expressions