lecture 27 notes added

resources/lecture-27/README.md

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+# Lecture 27 - Frontend Core Concepts and Communication
+
+### Who is our client?
+
+- device, browser, mobile, IOT are our clients.
+
+- In fact, Everything that can take JSON data is our CLIENT and that is mostly FRONTEND
+
+![Structure-diagram](./structure_diagram.png)
+
+### What is located in the FRONTEND:
+
+- Representation layer - what we see or the actual UI and get the feedback from the user
+- Data layer -  where we will manage our Data. these are two types: application data and backend or server data
+- Logical Layer - takes input from the Data Layer and changes the Representation Layer according to the data changes and Vice versa. The logical Layer combines every other layer
+- Network Layer - Will be connected with Logical Layer and connect the frontend with the backend and server
+
+NOTE: **This is applicable for all frontend applications**
+
+IF our backend server collects data from other servers then our backend server works as a frontend
+
+### React
+Mind map:
+![Structure-diagram](./react.png)