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Service Definition

Service Views

Business view

A service realizes an effect that brings a business value to a service consumer

for example, to pay for and deliver a book

Conceptual view

encapsulation, reusability, loose coupling, contracting, abstraction,
discoverability, composability

Logical view

service interface, description and implementation
message-oriented and resource-oriented

Software architecture view

business service (also application service)

external, exposed functionality of an application

middleware service

internal/technical, supports processing of requests

Technology architecture view

REST/RESTful, GraphQL
XML-RPC/SOAP, RMI, gRPC
WebSocket, WebRTC, SSE

Interface, Description and Implementation

Terminology clarification

service ~ service interface + service implementation
WSDL service ~ service description in WSDL language
SOAP service ~ a service interface is possible to access through SOAP protocol; there is a WSDL description usually available too.
REST/RESTful service ~ service interface that conforms to REST architectural style and HTTP protocol
Microservice ~ a set of services that realize an app's capability

Service Interface

Service interface components

Data

Data model definition used by the service
for example, input and output messages, representation of resources

Functions

operations and input and output data used by operations

Process

public process: how to consume the service's functionality

Technical

security, usage aspects (SLA-Service Level Agreement)
other technical details such as IP addresses, ports, protocols, etc.

Public Process

A state diagram

operation of a service defines a state transition between two states.

Service Characteristics

Integrating Applications

Integration and Interoperability

Integration

A process of connecting applications so that they can exchange and share capabilities, that is — information and functionalities.
Includes methodological approaches as well as technologies

Interoperability

Ability of two or more applications to understand each other
Interoperability levels

Data – syntax/structure and semantics
Functions/Processes – syntax and semantics
Technical aspects – protocols, network addresses, etc.

Service Oriented Architecture

SOA supports two core business strategies

Growing top-line revenue

Enterprise reacts quickly to requirements from the market
Business processes can be reconfigured rather than reimplemented

Improving bottom-line profit

Saving development costs by resuing existing services

Pre-integrated solutions

Out-of-the-box applications and integration solutions among them

One-to-One Service Integration

Direct integration of applications

Multiple protocols problem, multiple vendor problem
Replication of integration functionalities such as interoperability solutions

Many-to-Many Service Integration

Enterprise Service Bus – central integration technology

Realizes so called Service Oriented Architecture (SOA)
Contains various integration components such as process server, mediators, messaging middleware, identity management, etc.

Integration Approaches Overview

Data-oriented Integration

Third-party database access

Application D accesses a database of application B directly by using SQL and a knowledge of database B structure and constraints
In the past: monolithic and two-tier client/server architectures
Today: ETL (Extract, Transform, Load) technologies

Problems

App D must understand complex structures and constraints

Data – very complex, includes structure and integrity constraints
Functions/processes – hidden in integrity constraints
Technical – access mechanisms can vary

Service-oriented Integration

Integration at the application layer

Application exposes services that other applications consume
Services hide implementation details but only define interfaces for integration

Problems

Can become unmanageable if not properly designed
Interoperability

Data – limited to input and output messages only
Functions/processes – limited to semantics of services
Technical – access mechanisms can vary

Integration and Types of Data

Real-time data – Web services

Service-oriented integration
online, realtime communication between a client and a service
Usually small data and small amount of service invocation in a process

Bulk data – ETL

Data-oriented integration
processing of large amount of data in batches
Sometimes required for reconciliation across apps

when real-time integration fails and there is poor error handling

SOA provides both Web service and ETL capabilities

Enterprise Service Bus

ESB is a central intermediary in SOA

Types of services: shared and infrastructure
Types of processes: Technical and Business

ESB Application

Application running on an application server
Exposes functionality via Web service interface
Allows to communicate with various messaging protocols

Middlware Integration Patterns

Technical-level interoperability – message broker
Location transparency
Dynamic routing
Session pooling
Message enrichment
Data transformation
Key mapping

Integration Patterns

Synchronous and Asynchronous Integration

Synchronous and Asynchronous Integration

Synchronous

one socket, |t_req – t_res| is small
easy to implement and deploy, only standard firewall config
only the server defines endpoint

Asynchronous

request, response each has socket, client and server define endpoints
|t_req – t_res| can be large (hours, even days)
harder to do across network elements (private/public networks issue)

Asynchronous via Intermediary

Intermediary

A component that decouples a client-server communication
It increases reliability and performance

The server may not be available when a client sends a request
There can be multiple servers that can handle the request

Further Concepts

Message Queues (MQ) – queue-based communication
Publish/Subscribe (P/S) – event-driven communication

Asynchronous via Polling

Polling – only clients open sockets

A client performs multiple request-response interactions

The first interaction initiates a process on the server
Subsequent interactions check for the processing status
The last interaction retrieves the processing result

Properties of environments

A server cannot open a socket with the client (network restrictions)
Typically on the Web (a client runs in a browser)

Microservices Architecture

The Scale Cube

Three-dimensional scalability model

X-Axis scaling requests across multiple instances
Y-Axis scaling decomposes an application into micro-services
Z-Axis scaling requests across "data partitioned" instances

Overview

Emerging software architecture

monolithic vs. decoupled applications
applications as independenly deployable services

Major Characteristics

Loosely coupled

Integrated using well-defined interfaces

Technology-agnostic protocols

HTTP, they use REST architecture

Independently deployable and easy to replace

A change in small part requires to redeploy only that part

Organized around capabilities

such as accounting, billing, recommendation, etc.

Impplemented using different technologies

polyglot – programming languages, databases

Owned by a small team