Platform Team/Sugar Network/Architecture

This is a twin page of Sugar Network's basic concepts from technical point of view. See also the introduction page.

Overview

Functioning

The only worfklow within the Sugar Network from the technical point of view is:

• Clients create, modify and browse different types of resources (resources from conceptual point of view, resources from the API point of view) on a server;
• If this server is a Node server, the system will take care about synchronizing its resources with other Node servers and, finally, with the central one, the Master server.

Components

This is technical view on three levels of the Sugar Network:

• Server side,
• Conceptual level,
• Client side.

Server

Server side is represented by:

• Master server that keeps the whole Sugar Network information, clients might connect directly to this server (on-line case) or indirectly via Node servers (off-line case);
• Optional Node servers, contain a synchronised copy of central server (might be not for the entire Network to save storage space);

In all cases the server API is the same for clients. But depending on connectivity, clients might be connected to the Master server or to a intermediate server.

Master server

The place where data is being collected from all Node servers. If clients have connectivity, they can connect to the Master to contribute to the Network directly.

Node servers

Servers that will be useful if:

• there is no connectivity at all;
• connectivity is sporadic;
• connectivity is not cheap and its usage needs to be minimized.

Node servers provide full featured API as the Master does. Nodes need to be synchronized.

Synchronisation

To let Network participant, connected to particular Node server, interact with people from another Node servers or with people from the Internet, Node servers need to be synchronized.

Server might be synchronised:

• With the Master, if connectivity presents;
• With the Master or any other Node servers via the Sneakernet.

Conceptual level

This is how Sugar Network looks like on conceptual level represented by the API.

Objects model

The following diagram shows the full list of objects implemented by the Sugar Network API.

Sugar Network objects

Resource.layers

This is an attempt to generalize the idea of user/resource levels with idea that objects should not be removed from the Network immediately (only hidden, and permanently removed by Network administrators). So, every resource is associated with a layer, i.e., it might be visible for observers only if they requested this layer and have permissions to see it.

For now, implemented only the following list of layers, but it might be reused for teachers related workflows later:

• public, object is visible for everyone;
• deleted Network objects' layer will be changed to deleted after removing objects by users.

Context.type

Context types:

• application, software application;
• library, software library;
• activity, Sugar activity;
• article, arbitrary content in a form of article.

Implementation.license

Short license names. The licenses should conform with the Activity Library licensing policy.

Implementation.stability

Stability level of the Implementation. Values conform to 0install stability levels and could be:

• insecure,
• buggy,
• developer,
• testing,
• stable.

Artifact.type

The type of the Artifact:

• screenshot, screenshot generated within the Context;
• jobject, Journal object generated by Sugar activity.

Notification.type

• create, object was created;
• update, object's properties were modified;
• delete, object was deleted (hidden);
• vote, object was voted/unvoted.

The model refers to the following additional information:

Simplified editing workflow

The system is designed to be as lightweight as possible to make it running on XO laptops in unmaintainable environments and simplify synchronization. So, the following design decisions were taken:

• No history for Sugar Network objects, only events about made changes;
• Only object author(s) can process editing;
• But, other people can suggest changes (that might be implemented on client side in pretty powerful way, e.g., people can change objects but it will be postponed for later author(s)' review).

That might be changed but only after making system one level more complicated.

Client

This is what Network participants are interacting with. This is a software that let people get access to the Sugar Network and define how Sugar Network should look like from users point of view. User experience, that these clients provide, might be too different from a client to a client. Starting from a couple of elements in the already existing software's GUI (when people even don't suspect they are interacting with the Sugar Network) and ending with clients that represent conceptual level as close as possible.

Client side is represented by:

• Client application that uses API to interact with a server;
• Client application that provides limited API to support server-less workflow.

Client application is local, for reasons:

• Originally, Sugar Network was being developed for deployments where teachers' XOs will be Node servers, thus, it will be useful to delegate some of computing to students' XOs;
• Stimulate doing behaviour when it should be possible to create new client application or tweak existing on a client side;
• It is all time possible to create Web application on a server side.

Personal server

This local application provides limited API to get access to:

• Private data in user's home directory,
• Data accessible from removable devices like USB sticks or SD cards.

Implementations

• Mejorar Sistema.

Getting involved

• Submit your bug report or feature request.
• Browse our implementation discussions, and post your feedback. (You should join this discussion list in order to avoid having your messages postponed for moderation.)

References

• An OLPC wiki page about the Sneakernet.