UOPeople Software Engineering 1 Flashcards

Question

When should you consider using Domain Driven Design pattern?

Answer 1

Consider DDD if you have a complex domain and you wish to improve communication and understanding within your development team, or where you must express the design of an application in a common language that all stakeholders can understand. DDD can also be an ideal approach if you have large and complex enterprise data scenarios that are difficult to manage using other techniques.

Answer 2

Consider the component-based architectural style if you already have suitable components or can obtain suitable components from third-party suppliers; your application will predominantly execute procedural-style functions, perhaps with little or no data input; or you want to be able to combine components written in different code languages. Also, consider this style if you want to create a pluggable or composite architecture that allows you to easily replace and update individual components.

Answer 3

1. Monolith 2. Component-Based (CBA) 3. Client/Server 3. Domain-Driven Design (DDD) 5. Layered Architecture 6. Message Bus 7. N-Tier 8. Object-Oriented (OOD) 9. Services-Oriented Architecture (SOA)

Answer 4

``` Presentation Service Business logic Persistence database/infrastructure ```

Answer 5

1. N-tier 2. Cached 3. Open/Closed

Answer 6

Separation of concerns. Separated Presentation patterns divide UI processing concerns into distinct roles; for example, MVC has three roles: the Model, the View, and the Controller. The Model represents data (perhaps a domain model that includes business rules); the View represents the UI; and the Controller handles requests, manipulates the model, and performs other operations. Event-based notification. The Observer pattern is commonly used to provide notifications to the View when data managed by the Model changes. Delegated event handling. The controller handles events triggered from the UI controls in the View.

Answer 7

Consider the layered architectural style if you have existing layers that are suitable for reuse in other applications, you already have applications that expose suitable business processes through service interfaces, or your application is complex and the high-level design demands separation so that teams can focus on different areas of functionality. The layered architectural style is also appropriate if your application must support different client types and different devices, or you want to implement complex and/or configurable business rules and processes. Consider a Separated Presentation pattern if you want improved testability and simplified maintenance of UI functionality, or you want to separate the task of designing the UI from the development of the logic code that drives it. These patterns are also appropriate when your UI view does not contain any request processing code, and does not implement any business logic.

Answer 8

Enterprise Service Bus (ESB). Based on message bus designs, an ESB uses services for communication between the bus and components attached to the bus. An ESB will usually provide services that transform messages from one format to another, allowing clients that use incompatible message formats to communicate with each other Internet Service Bus (ISB). This is similar to an enterprise service bus, but with applications hosted in the cloud instead of on an enterprise network. A core concept of ISB is the use of Uniform Resource Identifiers (URIs) and policies to control the routing of logic through applications and services in the cloud.

Answer 9

Consider the message bus architectural style if you have existing applications that interoperate with each other to perform tasks, or you want to combine multiple tasks into a single operation. This style is also appropriate if you are implementing a task that requires interaction with external applications, or applications hosted in different environments.

Answer 10

Consider either the N-tier or the 3-tier architectural style if the processing requirements of the layers in the application differ such that processing in one layer could absorb sufficient resources to slow the processing in other layers, or if the security requirements of the layers in the application differ. For example, the presentation layer should not store sensitive data, while this may be stored in the business and data layers. The N-tier or the 3-tier architectural style is also appropriate if you want to be able to share business logic between applications, and you have sufficient hardware to allocate the required number of servers to each tier. Consider using just three tiers if you are developing an intranet application where all servers are located within the private network; or an Internet application where security requirements do not restrict the deployment of business logic on the public facing Web or application server. Consider using more than three tiers if security requirements dictate that business logic cannot be deployed to the perimeter network, or the application makes heavy use of resources and you want to offload that functionality to another server

Answer 11

Understandable. It maps the application more closely to the real world objects, making it more understandable. Reusable. It provides for reusability through polymorphism and abstraction. Testable. It provides for improved testability through encapsulation. Extensible. Encapsulation, polymorphism, and abstraction ensure that a change in the representation of data does not affect the interfaces that the object exposes, which would limit the capability to communicate and interact with other objects. Highly Cohesive. By locating only related methods and features in an object, and using different objects for different sets of features, you can achieve a high level of cohesion.

Answer 12

Consider the object-oriented architectural style if you want to model your application based on real world objects and actions, or you already have suitable objects and classes that match the design and operational requirements. The object-oriented style is also suitable if you must encapsulate logic and data together in reusable components or you have complex business logic that requires abstraction and dynamic behavior.

Answer 13

Atomic: Well defined and self-contained, do not rely on other services Composite: composition of two or more atomic services, which depends on each other

Answer 14

Frontend: terminals, service consumers, etc Integration: gateways, adapters, etc Business: business functionality Public Enterprise: security, authentication, etc Infrastructure: event logging etc

Answer 15

Enterprise Service Bus: Could be a single server or some complex middleware, it is responsible for handling the integration part of the system

Answer 16

Service Description Repository/Registery How consumers of a service discore services and how to connect with them

Answer 17

Consider the SOA style if you have access to suitable services that you wish to reuse; can purchase suitable services provided by a hosting company; want to build applications that compose a variety of services into a single UI; or you are creating Software plus Services (S+S), Software as a Service (SaaS), or cloud-based applications. The SOA style is suitable when you must support message-based communication between segments of the application and expose functionality in a platform independent way, when you want to take advantage of federated services such as authentication, or you want to expose services that are discoverable through directories and can be used by clients that have no prior knowledge of the interfaces.

Answer 18

Creational Patterns: These design patterns provide ways to create objects while hiding the creation logic, instead of instantiating objects directly using the new operator. This gives the program more flexibility in deciding which objects need to be created for a given use case. Structural Patterns: These design patterns deal with class and object composition. The concept of inheritance is used to compose interfaces and define ways to compose objects to obtain new functionality. Behavioral Patterns: These design patterns are specifically concerned with communication between objects.

Answer 19

Creational Patterns: These design patterns provide ways to create objects while hiding the creation logic, instead of instantiating objects directly using the new operator. This gives the program more flexibility in deciding which objects need to be created for a given use case. Abstract Factory. The abstract factory pattern is used to provide a client with a set of related or dependant objects. The "family" of objects created by the factory are determined at run-time. Builder. The builder pattern is used to create complex objects with constituent parts that must be created in the same order or using a specific algorithm. An external class controls the construction algorithm. Factory Method. The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time. Prototype. The prototype pattern is used to instantiate a new object by copying all of the properties of an existing object, creating an independent clone. This practise is particularly useful when the construction of a new object is inefficient. Singleton. The singleton pattern ensures that only one object of a particular class is ever created. All further references to objects of the singleton class refer to the same underlying instance.

Answer 20

Structural Patterns: These design patterns deal with class and object composition. The concept of inheritance is used to compose interfaces and define ways to compose objects to obtain new functionality. Adapter. The adapter pattern is used to provide a link between two otherwise incompatible types by wrapping the "adaptee" with a class that supports the interface required by the client. Bridge. The bridge pattern is used to separate the abstract elements of a class from the implementation details, providing the means to replace the implementation details without modifying the abstraction. Composite. The composite pattern is used to create hierarchical, recursive tree structures of related objects where any element of the structure may be accessed and utilised in a standard manner. Decorator. The decorator pattern is used to extend or alter the functionality of objects at run-time by wrapping them in an object of a decorator class. This provides a flexible alternative to using inheritance to modify behaviour. Facade. The facade pattern is used to define a simplified interface to a more complex subsystem. Flyweight. The flyweight pattern is used to reduce the memory and resource usage for complex models containing many hundreds, thousands or hundreds of thousands of similar objects. Proxy. The proxy pattern is used to provide a surrogate or placeholder object, which references an underlying object. The proxy provides the same public interface as the underlying subject class, adding a level of indirection by accepting requests from a client object and passing these to the real subject object as necessary.

Answer 21

Behavioral Patterns: These design patterns are specifically concerned with communication between objects. Chain of Responsibility. The chain of responsibility pattern is used to process varied requests, each of which may be dealt with by a different handler. Command. The command pattern is used to express a request, including the call to be made and all of its required parameters, in a command object. The command may then be executed immediately or held for later use. Interpreter. The interpreter pattern is used to define the grammar for instructions that form part of a language or notation, whilst allowing the grammar to be easily extended. Iterator. The iterator pattern is used to provide a standard interface for traversing a collection of items in an aggregate object without the need to understand its underlying structure. Mediator. The mediator pattern is used to reduce coupling between classes that communicate with each other. Instead of classes communicating directly, and thus requiring knowledge of their implementation, the classes send messages via a mediator object. Memento. The memento pattern is used to capture the current state of an object and store it in such a manner that it can be restored at a later time without breaking the rules of encapsulation. Observer (pub/sub). The observer pattern is used to allow an object to publish changes to its state. Other objects subscribe to be immediately notified of any changes. State. The state pattern is used to alter the behaviour of an object as its internal state changes. The pattern allows the class for an object to apparently change at run-time. Strategy. The strategy pattern is used to create an interchangeable family of algorithms from which the required process is chosen at run-time. Template Method. The template method pattern is used to define the basic steps of an algorithm and allow the implementation of the individual steps to be changed. Visitor. The visitor pattern is used to separate a relatively complex set of structured data classes from the functionality that may be performed upon the data that they hold.