Catalog of Patterns of Enterprise Application Architecture
Enterprise applications are about the display, manipulation, and storage of large amounts of often complex data; together with the support or automation of business processes with that data. Examples include reservation systems, financial systems, supply chain systems, and many others that run modern business. Enterprise applications have their own particular challenges and solutions, and they are different from embedded systems, control systems, telecoms, or desktop productivity software.
The book Patterns of Enterprise Application
Architecture collects together patterns that I, and my colleagues,
have seen in these systems over the years. They include such topics as
layering, structuring business logic, structuring a web user interface,
linking in-memory data to a relational database, and handling session state
in stateless environments. This site contains short summaries of these
patterns, with deep links to the relevant chapters for the online eBook publication on
oreilly.com (marked on this page with 
).
Domain Logic Patterns
Transaction Script
Organizes business logic by procedures where each procedure handles a single request from the presentation.
Domain Model
An object model of the domain that incorporates both behavior and data.
Table Module
A single instance that handles the business logic for all rows in a database table or view.
Service Layer
Defines an application's boundary with a layer of services that establishes a set of available operations and coordinates the application's response in each operation.
Data Source Architectural Patterns
Table Data Gateway
An object that acts as a gateway to a database table. One instance handles all the rows in the table.
Row Data Gateway
An object that acts as a gateway to a single record in a data source. There is one instance per row.
Active Record
An object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.
Data Mapper
A layer of mappers that moves data between objects and a database while keeping them independent of each other and the mapper itself.
Object-Relational Behavioral Patterns
Unit of Work
Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems.
Identity Map
Ensures that each object gets loaded only once by keeping every loaded object in a map. Looks up objects using the map when referring to them.
Lazy Load
An object that doesn't contain all of the data you need but knows how to get it.
Object-Relational Structural Patterns
Identity Field
Saves a database ID field in an object to maintain identity between an in-memory object and a database row.
Inheritance Mappers
A structure to organize database mappers that handle inheritance hierarchies.
Foreign Key Mapping
Maps an association between objects to a foreign key reference between tables.
Association Table Mapping
Saves an association as a table with foreign keys to the tables that are linked by the association.
Dependent Mapping
Has one class perform the database mapping for a child class.
Embedded Value
Maps an object into several fields of another object's table.
Serialized LOB
Saves a graph of objects by serializing them into a single large object (LOB), which it stores in a database field.
Single Table Inheritance
Represents an inheritance hierarchy of classes as a single table that has columns for all the fields of the various classes.
Class Table Inheritance
Represents an inheritance hierarchy of classes with one table for each class.
Concrete Table Inheritance
Represents an inheritance hierarchy of classes with one table per concrete class in the hierarchy.
Object-Relational Metadata Mapping Patterns
Metadata Mapping
Holds details of object-relational mapping in metadata.
Query Object
An object that represents a database query.
Repository
Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.
Web Presentation Patterns
Model View Controller
Splits user interface interaction into three distinct roles.
Page Controller
An object that handles a request for a specific page or action on a Web site.
Front Controller
A controller that handles all requests for a Web site.
Template View
Renders information into HTML by embedding markers in an HTML page.
Transform View
A view that processes domain data element by element and transforms it into HTML.
Two Step View
Turns domain data into HTML in two steps: first by forming some kind of logical page, then rendering the logical page into HTML.
Application Controller
A centralized point for handling screen navigation and the flow of an application.
Distribution Patterns
Remote Facade
Provides a coarse-grained facade on fine-grained objects to improve efficiency over a network.
Data Transfer Object
An object that carries data between processes in order to reduce the number of method calls.
Offline Concurrency Patterns
Optimistic Offline Lock
Prevents conflicts between concurrent business transactions by detecting a conflict and rolling back the transaction.
Pessimistic Offline Lock
Prevents conflicts between concurrent business transactions by allowing only one business transaction at a time to access data.
Coarse-Grained Lock
Locks a set of related objects with a single lock.
Implicit Lock
Allows framework or layer supertype code to acquire offline locks.
Session State Patterns
Client Session State
Stores session state on the client.
Server Session State
Keeps the session state on a server system in a serialized form
Database Session State
Stores session data as committed data in the database.
Base Patterns
Gateway
An object that encapsulates access to an external system or resource.
Service Stub
Removes dependence upon problematic services during testing. WSDL
Record Set
An in-memory representation of tabular data.
Mapper
An object that sets up a communication between two independent objects.
Layer Supertype
A type that acts as the supertype for all types in its layer.
Separated Interface
Defines an interface in a separate package from its implementation.
Registry
A well-known object that other objects can use to find common objects and services.
Value Object
A small simple object, like money or a date range, whose equality isn't based on identity.
Money
Represents a monetary value.
Special Case
A subclass that provides special behavior for particular cases.
Plugin
Links classes during configuration rather than compilation.
Notes
This page had a design refresh in July 2024, but the content is still the same as its original 2003 publication.
Many of these sketch diagrams in the patterns demonstrate the rather poor GIF output of Visio at that time. The nice diagrams were redrawn for me by David Heinemeier Hansson