README.md: Add EDDIE structure section and build prerequisites

- Add EDDIE structure section
- add build prerequisites section
- add reference to doxygen docs

Signed-off-by: Jacopo Zorzetto <jacopo.zorzetto@mail.polimi.it>
Signed-off-by: Francesco Pham <francesco.pham@huawei.com>

Co-authored-by: Jacopo Zorzetto <jacopo.zorzetto@mail.polimi.it>

README.md

@@ -35,8 +35,90 @@ See the `LICENSES` subdirectory.
 
 See the `SECURITY.md` file.
 
+## EDDIE structure
+The structure of the EDDIE project is vertically divided into layers and
+this division reflects the structure of the EDDIE repository.
+
+While the communication and the virtualization layer are detailed below and already present in the EDDIE repository,
+an intelligent layer is planned, to enable reasoning and smart resource distribution across the EDDIE network.
+Currently, there is only a mocked version of this layer.
+
+Lastly an application management layer is also planned, providing advanced functionalities for process management
+in both local and remote EDDIE nodes.
+
+### Layers
+In the following paragraphs there is a more detailed description of the layers of EDDIE.
+
+- **Communication Layer**
+
+The bottommost component of EDDIE is the communication layer: it is responsible for all the networking bits of EDDIE,
+from the creation and setup of the connection to the message dispatching to other nodes.
+
+Every device that runs EDDIE has a server component, application logic that describes what capabilities (resources) that device has and answers to requests from other nodes.  
+Alongside the server element, a EDDIE device is equipped with a client component, allowing the device to comunicate actively in the network, performing requests to other devices.
+
+Additionally, one node in the EDDIE network is elected as Resource Directory (RD): a new EDDIE node that wants to connect to the network should post its resources description in the RD, while from the RD it can retreive the descriptions of other nodes.
+
+The communication layer exposes a list of APIs to the higher layers of EDDIE, allowing complex actions and queries to be executed in the EDDIE network.
+
+- **Virtualization layer**
+
+The Virtualization layer is responsible for the interaction between the EDDIE network (through the communication layer) and the single EDDIE-enabled application running on the device.
+
+This layer is composed of two elements that are communicating through the IPC mechanism of d-bus:
+- a receiver component that exposes its API on d-bus, allowing multiple applications to interact with EDDIE at the same time.
+The API is composed of a single function `PerformAction` that models the action that the application wants to execute on the network, like changing or getting the status of a resource.
+- a sender component is also present in the virtualization directory with the role of transmitting the requests generated by EDDIE-enabled application to the EDDIE service on the device.
+
+### Examples
+Examples on how to use the EDDIE APIs can be found in `/linux/examples`.
+
+For more details, take a look at the [doxygen API documentations](https://docs.svc.ostc-eu.dev/).
+
 ## Build instructions
-- If you want to run EDDIE on your local machine build the CMake project.
+
+### Prerequisites
+The following part of the document details how to install
+and configure all packages and libraries required to have
+a working copy of EDDIE.
+
+- libcoap
+
+libcoap is a C implementation of the application-level protocol CoAP.  
+The version of libcoap currently used by EDDIE is `version 4.3.0`.
+
+If libcoap is already installed in your system you can skip the following installation procedure. 
+
+libcoap itself requires some packages to correctly complete its installation procedure:
+they can be installed with the following commands:
+
+```console
+$ (sudo) apt-get install autoconf -y
+$ (sudo) apt-get install libtool -y
+```
+
+Then launch these commands to install libcoap in your machine:
+
+```console
+$ git clone https://github.com/obgm/libcoap.git
+$ git checkout release-4.3.0
+$ cd libcoap
+$ ./configure --disable-documentation --disable-dtls
+$ make
+$ (sudo) make install
+$ (sudo) ldconfig
+```
+For further details on libcoap have a look at the [github repository](https://github.com/obgm/libcoap)
+and at the [official libcoap documentation page](https://libcoap.net/).
+
+- Glib
+
+Installation instructions for Glib and its requirements can be found at the
+[Glib installation page](https://github.com/GNOME/glib/blob/main/INSTALL.md?plain=1).
+
+### Build
+- If you want to run EDDIE on your local machine build the CMake project:
+
 ```console
 $ mkdir build && cd build
 $ cmake ..
@@ -44,16 +126,16 @@ $ make
 ```
 - Then you can find some binaries in the `build/linux/` subdirectory:
   - `eddie-endpoint` is used to test the Eddie communication layer by 
-initializing an `EddieEndpoint` for the CoAP communication and resource 
+initializing an [EddieEndpoint](https://docs.svc.ostc-eu.dev/classEddieEndpoint.html) for the CoAP communication and resource 
 registration and discovery. In this executable 
 a resource directory discovery request is sent and if a one is not found, a new
 resource directory is initialized. If `--example-res` flag is set, the node will 
 publish some example resources, and finally, the node will retrieve the available
 resources in the resource directory. Run `eddie-endpoint --help` for more information.
   - `eddie-virt-server` runs a `VirtualizationReceiver` which starts a DBus 
-server and initializes an `EddieEndpoint`.
+server and initializes an [EddieEndpoint](https://docs.svc.ostc-eu.dev/classEddieEndpoint.html).
   - `eddie-virt-client` is an example of application side code that, 
 using `VirtualizationSender`, runs a DBus client to communicate with the 
 virtualization server side.
 
-- If you want to build the Oniro Blueprint for the EDDIE project, and run on an Oniro supported target: follow the instructions in the [EDDIE blueprint git repository](https://gitlab.eclipse.org/eclipse/oniro-blueprints/meta-oniro-blueprints-eddie).
\ No newline at end of file
+- If you want to build the Oniro Blueprint for the EDDIE project, and run on an Oniro supported target: follow the instructions in the [EDDIE blueprint git repository](https://gitlab.eclipse.org/eclipse/oniro-blueprints/meta-oniro-blueprints-eddie).