Enterprise Integration Patterns Flashcards
Message Channel
How does one application communicate with another using messaging?
How can two applications connected by a message channel exchange a piece of information?
Message
How can we perform complex processing on a message while maintaining independence and flexibility?
Pipes and Filters
How can you decouple individual processing steps so that messages can be passed to different filters depending on a set of conditions?
Message Router
How can systems using different data formats communicate with each other using messaging?
Message Translator
How does an application connect to a messaging channel to send and receive messages?
Message Endpoint
How can the caller be sure that exactly one receiver will receive the document or perform the call?
Point-to-Point Channel
How can the sender broadcast an event to all interested receivers?
Publish-Subscribe Channel
How can the application send a data item such that the receiver will know how to process it?
Datatype Channel
How can a messaging receiver gracefully handle receiving a message that makes no sense?
Invalid Message Channel
What will the messaging system do with a message it cannot deliver?
Dead Letter Channel
How can the sender make sure that a message will be delivered even if the messaging system fails?
Guaranteed Delivery
How can you connect an application to the messaging system so that it can send and receive messages?
Channel Adapter
How can multiple messaging systems be connected so that messages available on one are also available on the others?
Messaging Bridge
What is an architecture that enables separate applications to work together but in a decoupled fashion such that applications can be easily added or removed without affecting the others?
Message Bus
How can messaging be used to invoke a procedure in another application?
Command Message
How can messaging be used to transfer data between applications?
Document Message
How can messaging be used to transmit events from one application to another?
Event Message
When an application sends a message how can it get a response from the receiver?
Request-Reply
How does a replier know where to send the reply?
Return Address
How does a requestor that has received a reply know which request this is the reply for?
Correlation Identifier
How can messaging transmit an arbitrarily large amount of data?
Message Sequence
How can a sender indicate when a message should be considered stale and thus shouldn’t be processed?
Message Expiration
How can a message’s data format be designed to allow for possible future changes?
The format indicator enables the sender to tell the receiver the format of the message. This way, a receiver expecting several possible formats knows which one a message is using and therefore how to interpret the message’s contents.
There are three main alternatives for implementing a format indicator:
Version Number – A number or string that that uniquely identifies the format. Both the sender and receiver must agree on which format is designated by a particular indicator.
Foreign Key – A unique ID—such as a filename, a database row key, a home primary key, or an Internet URL—that specifies a format document. The sender and receiver must agree on the mapping of keys to documents, and the format of the schema document.
Format Document – A schema that describes the data format. The schema document does not have to be retrieved via a foreign key or inferred from a version number, it is embedded in the message. The sender and the receiver must agree on the format of the schema.
How do we handle a situation where the implementation of a single logical function (e.g. inventory check) is spread across multiple physical systems?
Content-Based Router
How can a component avoid receiving uninteresting messages?
Message Filter
How can you avoid the dependency of the router on all possible destinations while maintaining its efficiency?
Dynamic Router
During system start-up, each potential recipient sends a special message to the Dynamic Router on this control channel, announcing its presence and listing the conditions under which it can handle a message. The Dynamic Router stores the ‘preferences’ for each participant in a rule base. When a message arrives, the Dynamic Router evaluates all rules and routes the message to the recipient whose rules are fulfilled. This allows for efficient, predictive routing without the maintenance dependency of the Dynamic Router on each potential recipient.
How do we route a message to a list of dynamically specified recipients?
Recipient List
How can we process a message if it contains multiple elements each of which may have to be processed in a different way?
Splitter
How do we combine the results of individual but related messages so that they can be processed as a whole?
Aggregator
How can we get a stream of related but out-of-sequence messages back into the correct order?
Resequencer
How can you maintain the overall message flow when processing a message consisting of multiple elements each of which may require different processing?
Composed Message Processor
How do you maintain the overall message flow when a message needs to be sent to multiple recipients, each of which may send a reply?
Scatter-Gather
How do we route a message consecutively through a series of processing steps when the sequence of steps is not known at design-time and may vary for each message?
Routing Slip
Attach a Routing Slip to each message, specifying the sequence of processing steps. Wrap each component with a special message router that reads the Routing Slip and routes the message to the next component in the list.
How do we route a message through multiple processing steps when the required steps may not be known at design-time and may not be sequential?
Process Manager
Use a central processing unit, a Process Manager, to:
- maintain the state of the sequence and
- determine the next processing step based on intermediate results.
How can you decouple the destination of a message from the sender and maintain central control over the flow of messages?
Message Broker
How can existing systems participate in a messaging exchange that places specific requirements on the message format such as message header fields or encryption?
Envelope Wrapper
How do we communicate with another system if the message originator does not have all the required data items available?
Content Enricher
How do you simplify dealing with a large message when you are interested only in a few data items?
Content Filter
How can we reduce the data volume of message sent across the system without sacrificing information content?
Claim Check
How do you process messages that are semantically equivalent but arrive in a different format?
Normalizer
How can you minimize dependencies when integrating applications that use different data formats?
Canonical Data Model
How do you encapsulate access to the messaging system from the rest of the application?
Messaging Gateway
How do you move data between domain objects and the messaging infrastructure while keeping the two independent of each other?
Messaging Mapper
How can a client control its transactions with the messaging system?
Transactional Client
How can an application consume a message when the application is ready?
Polling Consumer
How can an application automatically consume messages as they become available?
Event-Driven Consumer
How can a messaging client process multiple messages concurrently?
Competing Consumers
How can multiple consumers on a single channel coordinate their message processing?
Message Dispatcher
How can a message consumer select which messages it wishes to receive?
Selective Consumer
How can a subscriber avoid missing messages while it’s not listening for them?
Durable Subscriber
How can a message receiver deal with duplicate messages?
Idempotent Receiver
How can an application design a service to be invoked both via various messaging technologies and via non-messaging techniques?
Service Activator
How can we effectively administer a messaging system that is distributed across multiple platforms and a wide geographic area?
Control Bus
How can you route a message through intermediate steps to perform validation testing or debugging functions?
Detour
How do you inspect messages that travel on a point-to-point channel?
Wire Tap
How can we effectively analyze and debug the flow of messages in a loosely coupled system?
Message History
How can we report against message information without disturbing the loosely coupled and transient nature of a messaging system?
Message Store
How can you track messages on a service that publishes reply messages to the Return Address specified by the requestor?
Smart Proxy
What can be used to validate a component that is actively processing messages but garbles outgoing messages due to an internal fault?
Test Message
Channel Purger
How can you keep ‘left-over’ messages on a channel from disturbing tests or running systems?
