SEMPR_ROS

This package contains tools to setup a sempr environment in ROS. It implements the sempr::gui::AbstractInterface with ros topics and services and thus can provide the equivalent of the sempr-gui-example-server and sempr-gui-example-client as ros nodes -- names sempr for the server and gui for the gui (obviously).

You'll probably want to implement your own sempr-environment-node for your use case and add specific interfaces and data to it. But if you just want to test the capabilities of sempr and/or need only a very basic version to model some rules and data, etc., you can use the nodes provided by this package.

SEMPR (server)

Take a look at launch/sempr.launch. This (very simple) launch file starts the server part of sempr, the actual reasoner etc., and can be configured with a path to a directory in which persistent data gets stored. The default value is sempr_data, which, when started through roslaunch, will lead to your data being stored in ~/.ros/sempr_data.

Every entity in sempr is stored in a separate file in the specified directory with the entity id as its name (so don't go crazy on the ids!). Manually deleting / cloning / ... an entity is as easy as deleting / copying / ... the file it's stored in. The format is json, so even editing is simple.

But manually editing files is no fun -- take a look at the gui instead.

ROS-Interface

Although the interface implemented here was primarly designed to suit the connection to the GUI, noone will stop you from using it in your nodes!

topic	description
sempr/ECUpdates	Publishes data whenever an Entity-Component-Pair changes. Beware that not all fields in the message will always be filled, e.g. when a component is removed only the entityId and componentId fields are set.
sempr/TripleUpdates	Publishes triples that are asserted or retracted

service	description
sempr/addEC	Adds a new component to an entity. The entity is created if it does not already exist. Only entityId and componentJSON are relevant. You do not get the id of the created component in return -- this is only sent through the topics.
sempr/modifyEC	Changes a component. Simply sets the newly given componentJSON value to the component identified through entityId and componentId.
sempr/removeEC	Removes the component identified by entityId and componentId.
sempr/listEC	Lists all entity-component information
sempr/listTriples	Lists all triples
sempr/listRules	Lists all rules
sempr/getReteNetwork	Returns a graph representation of the rete network, just for visualization as it only contains nodes with labels
sempr/explainEC	Returns a graph representing the paths on which the given EC was inferred. Only entityId and componentId need to be given.
sempr/explainTriple	Returns a graph representing the paths on which the given triple was inferred.

SEMPR-GUI (client)

Use rosrun sempr_ros gui to start the gui. This will wait for required services (which are provided by the server) in the sempr namespace.

Editing rules

There are exactly four rules loaded by default within the main sempr node:

• When an Entity-Component-Pair changes, notify the ROSConnectionServer
• When a Triple is inferred / retracted, notify the ROSConnectionServer

Note: The ROSConnectionServer is what provides the topics and services required by the GUI.

• Extract the Triples from TripleContainers.

Note: When specifying conditions on triples in your rules, e.g. (?x <type> ?y), these refer to rete::Triples which are "first-class" working memory elements (WMEs) in the reasoner. A TripleContainer is a component that holds information about any number of triples and is a WME on its own. In order to make use of the triples inside they need to be extracted and provided as WMEs to the reasoner -- and that's what this rule does.

• For every entity ?e with (?e <type> <Rules>) which has a TextComponent, interpret the text in it as a rule definition and add it to the reasoner.

The first two rules are needed to be able to work with the gui in general, and the remaining two are what enables you to add rules as data in the system. In order to add custom rules to a fresh, empty sempr instance, do the following:

1. Add a TriplePropertyMap to an entity, let's call it MyRules.
2. Edit the TriplePropertyMap: Add a new entry, with the property name being type, the value Rules and the type Resource. You'll need to specifiy that it is a Resource first, else whatever you insert as a value is converted to an integer (which is the default setting).

Note: This is what provides the (<MyRules> <type> <Rules>) triple.

1. Add a TextComponent to the same entity.
2. Define your rules in the newly create TextComponent

Note: You may add multiple TextComponents to the same entity to group your rules. Whenever a TextComponent is edited, all rules it defined before are removed and the new ones created, which also results in retracting all their consequences and re-inferring them.