Architectural Patterns

Question 1

What types of Architectural patterns (systems) are differentiated?

Answer 1

• Adaptable systems
• Interactive systems
• From Chaos to Structure systems
• Distributed Systems

Question 2

Name Adaptable systems:

Answer 2

• Dependency Injection

Question 3

Describe Dependency injection from the perspective of adaptable systems

Answer 3

• pattern provides an independent building block for the purpose of managing lifecycles of instances and deciding which specific classes are instantiated at runtime: assembler
• can be regarded as ‘universal factory’
• via meta-information specific implementations of abstract services are generated or determined

Question 4

Name interactive systems architecture patterns

Answer 4

• Model-View-Controller Pattern (MVC)
• Model-View-Presenter Pattern (MVP)
• Presentation-abstraction-control (PAC)

Question 5

Name Patterns to create structure from chaos

Answer 5

• Blackboard Pattern
• Layered-Architecture Pattern
• Pipes and Filters Pattern

Question 6

Describe the Layered Architecture Pattern

Answer 6

• layers of the same level of abstraction, encapsulate operations
• closed layers, so that effects of subsequent changes only affect that layer
• information exchange via interfaces, called services
• higher layer uses services provided by below layer
• communication across multiple layers is usually not permitted

Question 7

What can be drawbacks of a layered architecture?

Answer 7

• if requests are just passed through layers without additional logic a lot of unnecessary overhead is created
• adding a data field has a vertical effect, affecting all layers

Question 8

Describe the Pipes and Filters Pattern

Answer 8

• Filters transform data passed to them, processing units
• pipes work as conncetion between filters, data channels
• filters don’t know about other filters
• free sequencing of multiple filters and pipes independent of each other -> higher reusability

Question 9

What aspects are decoupled in a Pipes and Filters Pattern?

Answer 9

• chronologically (direct or time-shifted)
• transport mechanism / format
• dynamic determination of next filter: parallelism, load sharing, optional filters

Question 10

What can be drawbacks of the Pipes and Filters pattern?

Answer 10

• error states during can be complicated to deal with

Question 11

What are the Blackboard Pattern elements?

Answer 11

Three elements:
- blackboard
- KnowledgeSolution(s)
- Controller

Question 12

In the Blackboard Pattern, what is the Blackboard responsible for?

Answer 12

• manages the solutions approaches or solution elements of the Knowledge Sources

Question 13

In the Blackboard Pattern what are the KnowledgeSources?

Answer 13

• one or more independent KnowledgeSources
• analyze problems from a particular point of view and send solution proposals to Blackboard

Question 14

In the Blackboard Pattern what is the Controller?

Answer 14

• controler components
• monitors the Blackboard
• where necessary controls the execution of KnowledgeSources

Question 15

Describe the Blackboard Pattern

Answer 15

• complex problem with many facets gets analysed via multiple KnowledgeSources
• Blackboard is used to find best possible solution or solution-mix
• by KnowledgeSources proposed solutions can be approximate or incomplete

Question 16

What are examples for the Blackboard Pattern?

Answer 16

• image processing
• image recognition
• voice recognition
• system monitoring

Question 17

Describe challenges of distributed systems

Answer 17

• split-brain problem
• disrupted network connection can lead to inconsistencies
• failure handling needs to be explicitly addressed
• latendy is not stable
• exact temporal sequence of events is impossible to reconstruct

Question 18

What is the Split Brain problem in Distributed Systems?

Answer 18

• because of a network failure inconsistencies and problems may arise, what the true state of the system should be

Question 19

What Patterns are used in Distributed Systems?

Answer 19

• Broker pattern
• Service-Oriented Architecture
• modularization
• microservices

Question 20

Describe the Broker pattern

Answer 20

• only availability of another service is relevant for a system, not physical locality
• broker works as switching center for all other services, central point of communication
• services need to register with the broker
• requests are directed to broker, redirected by him to the target system
• responses flow again through the broker

Question 21

Describe the Service-Oriented Architecture Pattern

Answer 21

• services consume interfaces of each other after searching for target services in the service directory
• these interfaces are functional and have low-granularity
• interfaces are also contractual
• services should be idempotent, stateless, transactional, self-contained

Question 22

What are important roles in the Service Oriented Architecture Pattern?

Answer 22

Service Directory/directory service:
- publishes services registered by service providers

Service providers:
- offers services and registers them with directory service

Service Consumer:
- searches for services in service directory
- after finding them there calls their interfaces directly
- establishes a link with service provider

Question 23

How are Architecture Pattern and Design Patterns different?

Answer 23

• line is blurred
• Architectural patterns usually help in decomposition and composition of components
• Design patterns are more often used to support the implementation of functionality

Question 24

What is important about services in SOA?

Answer 24

each service:
- has a defined scope
- can be accessed from other components or services
- works as a module capable of delivering the input/output requested

Question 25

Describe how Resource oriented Architecture differs in terms of interface design from SOA

Answer 25

- api is decomposed in terms of resources first instead of services - often implemented in form of RESTful web services

Question 26

What important principle does Interface design follow? What does it say?

Answer 26

Principle of Information Hiding: - complexity of a system should be encapsulated - from outside seen as black-box - interaction only via defined interfaces - only subset of total information necessary for task should be disclosed

Question 27

In the Model-View-Controller Pattern, what are the tasks of the elements?

Answer 27

- Model: takes care of the data, encapsulates the business logic - View: manages the views on the model - Controller: processes user events, triggers updates of the view components

Question 28

How is the Model-View-Presenter pattern different than the Model-View-Controller?

Answer 28

- model is controlled by the presenter - model knows neither the view nor the presenter - view has extremely simple design - view contains no logic, solely responsible for the presentation and receipt of user input - presenter link view and model - controls logic flow between layers - collects all application use cases, accepts user input from view, calls methods in model, sets data in view

Question 29

What is the base principle of the Presentation-abstraction-Control (PAC)?

Answer 29

- structure of ai broken down into hierarchically cooperative 'agents' - each agents consists of controller, abstraction and view - controller is the agents interface to next higher- or lower-level agents and controls area of responsibility - functionality is provided my intermediate levels to lower-level UI elements