Lecture No. 03
Dated: 25-03-2025
The request-response looks as follows
sequenceDiagram
Order Processor ->> Inventory System: 1 Stock Query
Inventory System ->> Order Processor: 2 Stock QueryComparison
Events1 can be independent of the producer and consumer meanwhile we cannot say for sure about request response sequence, which reduces latency.
Events1 are one way (push), can have multiple consumers and can work asynchronously,1 reducing the coupling.
Event Channel
An event channel is a subscription mechanism for events.1
It can be an intermediary XML file.
Service Oriented Architecture
Service-oriented architecture (SOA) is built from request-response.
It moves away from monolithic applications.
Event Producer
An event producer is an entity at the edge of an event processing system that introduces events1 into the system.
Event Consumer
An event consumer is an entity at the edge of an event processing system that receives events1 from the system.
Raw Event
A raw event is an event1 that is introduced into an event processing system by an event producer.
Derived Event
A derived event is an event1 that is generated as a result of event processing that takes place inside an event processing system.
Stateless Event Processing
An event processing agent is said to be stateless if the way it processes one event1 does not influence the way it processes any subsequent events.1
Event Stream
An event stream is a set2 of associated events,1 which is often ordered.
Homogeneous
A stream in which all the events1 must be of the same type is called a homogeneous event stream.
Heterogeneous
A stream in which the events1 may be of different types is referred to as a heterogeneous event stream.
Types of Agents
- Filter
- Transformation
- Translate
- Enrich
- Project
- Aggregate
- Split
- Compose
- Translate
- Pattern detect
#include <iostream>
#include <fstream>
#include <conio.h>
int fileChanged = 0;
char lastChar = '-';
int onKeyPress() {
char b = std::cin.get();
std::cout << b << std::endl;
return b == 'x';
}
int onFileRead(char a) {
if (a != lastChar) {
fileChanged = 1;
lastChar = a;
}
return 0;
}
int onFileChanged() {
std::cout << lastChar << std::endl;
return lastChar == 'x';
}
int main() {
do {
if (_kbhit()) {
if (onKeyPress())
return 0;
}
std::ifstream f("test.txt", std::ifstream::in);
if (f.good()) {
if (onFileRead(f.get()))
return 0;
}
f.close();
if (fileChanged) {
if (onFileChanged())
return 0;
}
} while (true);
return 0;
}