Rules¶
Graph rewriting rules.
This package contains the Rule data structure for representation of graph rewriting rules (for more on sesqui-pushout rewriting see: https://link.springer.com/chapter/10.1007/11841883_4).
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class
regraph.rules.Rule(p=None, lhs=None, rhs=None, p_lhs=None, p_rhs=None)[source]¶ Class representing rewriting rules.
A rewriting rule consists of the three graphs: p – preserved part (or interface), lhs – left hand side, rhs – right hand side, and two mappings: from p to lhs and from p to rhs. Informally, lhs represents a pattern to match in a graph, subject to rewriting. p together with p -> lhs mapping specifies a part of the pattern which stays preseved during rewriting, i.e. all the nodes/edges/attributes present in lhs but not p will be removed. rhs and p -> rhs specify nodes/edges/attributes to add to the p. In addition, rules defined is such a way allow to clone and merge nodes. If two nodes from p map to the same node in lhs, the node corresponding to this node of the pattern will be cloned. Symmetrically, if two nodes from p map to the same node in rhs, the corresponding two nodes will be merged.
- Attributes
- pregaph.graphs.Graph
Preserved part of the rule
- lhsregaph.graphs.Graph
Left-hand side (pattern) of the rule
- rhsregaph.graphs.Graph
Right-hand side of the rule
- p_lhsdict
Homomorphism between p and lhs given by a dictionary with keys – nodes of p, values – nodes of lhs.
- p_rhsdict
Homomorphism between p and rhs given by a dictionary with keys – nodes of p, values – nodes of rhs.
Methods
added_edge_attrs(self)Get edge attributes added by the rule.
added_edges(self)Get edges added by the rule.
added_node_attrs(self)Get node attributes added by the rule.
added_nodes(self)Get nodes added by the rule.
cloned_nodes(self)Get nodes cloned by the rule.
from_json(json_data)Create a rule obj from JSON repr.
from_transform(pattern[, commands])Initialize a rule from the transformation.
get_inverted_rule(self)Get inverted rule with LHS and RHS swaped.
Create an identity rule.
inject_add_edge(self, n1, n2[, attrs])Inject addition of a new edge to the rule.
inject_add_edge_attrs(self, n1, n2, attrs)Inject addition of edge attributes by the rule.
inject_add_edges_from(self, edge_list)Inject addition of a new edge to the rule.
inject_add_node(self, node_id[, attrs])Inject an addition of a new node by the rule.
inject_add_node_attrs(self, n, attrs)Inject addition of node attributes by the rule.
inject_add_nodes_from(self, node_list)Inject an addition of a new node by the rule.
inject_clone_node(self, n[, new_node_id])Inject cloning of a node by the rule.
inject_merge_nodes(self, node_list[, node_id])Inject merge of a collection of nodes by the rule.
inject_remove_edge(self, n1, n2)Inject removal of an edge by the rule.
inject_remove_edge_attrs(self, n1, n2, attrs)Inject a removal of edge attrs by the rule.
inject_remove_node(self, p_node_id)Inject a new node removal to the rule.
inject_remove_node_attrs(self, n, attrs)Inject a removal of node attrs by the rule.
inject_update_edge_attrs(self, n1, n2, attrs)Inject an update of edge attrs by the rule.
inject_update_node_attrs(self, n, attrs)Inject an update of node attrs by the rule.
is_identity(self)Test if the rule is identity.
is_relaxing(self)Check if the rule is relaxing.
is_restrictive(self)Check if the rule is restrictive.
merged_nodes(self)Get nodes merged by the rule.
plot(self[, filename, title])Plot the rule.
refine(self, graph, instance)Get refined (side-effect-free) version of the rule.
removed_edge_attrs(self)Get edge attributes removed by the rule.
removed_edges(self)Get edges removed by the rule.
removed_node_attrs(self)Get node attributes removed by the rule.
removed_nodes(self)Get nodes removed by the rule.
to_commands(self)Convert the rule to a list of commands.
to_json(self)Convert the rule to JSON repr.
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added_edge_attrs(self)[source]¶ Get edge attributes added by the rule.
- Returns
- attrsdict
Dictionary where keys are edges from rhs and values are attribute dictionaries to add.
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added_edges(self)[source]¶ Get edges added by the rule.
- Returns
- edgesset
Set of edges from rhs added by the rule.
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added_node_attrs(self)[source]¶ Get node attributes added by the rule.
- Returns
- attrsdict
Dictionary where keys are nodes from rhs and values are attribute dictionaries to add.
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added_nodes(self)[source]¶ Get nodes added by the rule.
- Returns
- nodesset
Set of nodes from rhs added by the rule.
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cloned_nodes(self)[source]¶ Get nodes cloned by the rule.
- Returns
- nodesdict
Dictionary where keys are nodes from lhs and values are sets of corresponding nodes from p.
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classmethod
from_transform(pattern, commands=None)[source]¶ Initialize a rule from the transformation.
On input takes a pattern which is used as lhs of the rule, as an optional argument transformation commands can be provided, by default the list of commands is empty and all p, lhs and rhs are initialized to be the same graph (pattern), later on when transformations are applied p and rhs are being updated. If list of commands is specified, these commands are simplified, transformed to the canonical order, and applied to p, lhs and rhs.
- Parameters
- patternnetworkx.(Di)Graph
Pattern graph to initialize and the lhs of the rule.
- commandsstr, optional
Script containing transformation commands, which can be parsed by regraph.parser.parse.
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inject_add_edge(self, n1, n2, attrs=None)[source]¶ Inject addition of a new edge to the rule.
This method adds an edge between two nodes of the rhs.
- Parameters
- n1hashable
Id of an edge’s source node in rhs.
- n2hashable
Id of an edge’s target node in rhs.
- Raises
- RuleError
If some of the nodes (n1 or n2) do not exist or if there is already an edge between them in rhs.
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inject_add_edge_attrs(self, n1, n2, attrs)[source]¶ Inject addition of edge attributes by the rule.
- Parameters
- n1hashable
Source node in the RHS
- n2hashable
Target node in the RHS
- attrsdict
Dictionary with attrs to add
- Raises
- RuleError
If some of the nodes defining an edge are not found in neither rhs, or if an edge is incident to smth thats is going to be removed by the rule.
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inject_add_edges_from(self, edge_list)[source]¶ Inject addition of a new edge to the rule.
This method injects addition of edges from the list.
- Parameters
- edge_listiterable
Collection of edges to add, where every element is either a tuple of the form (<source_id>, <target_id>) or (<source_id>, <target_id>, <edge_attrs>). Here source and target nodes are assumed to be from the rhs.
- Raises
- RuleError
If some of the nodes (n1 or n2) do not exist or if there is already an edge between them in rhs.
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inject_add_node(self, node_id, attrs=None)[source]¶ Inject an addition of a new node by the rule.
This method adds a node with node_id (and the specified attributes attrs) to rhs.
- Parameters
- node_idhashable
Id of a node to add
- attrsdict, optional
Attributes of the node.
- Raises
- RuleError
If node with this id already exists in the rhs.
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inject_add_node_attrs(self, n, attrs)[source]¶ Inject addition of node attributes by the rule.
- Parameters
- nhashable
Id of the node in the rhs to add attributes to.
- attrsdict
Dictionary with attrs to add
- Raises
- RuleError
If node n does not exist in the rhs of the rule
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inject_add_nodes_from(self, node_list)[source]¶ Inject an addition of a new node by the rule.
This method adds a nodes from the list (and the specified attributes attrs) to rhs.
- Parameters
- node_listiterable
Collection of nodes to add, where every element is either a tuple of the form (<node_id>, <node_attrs>) or a single value <node_id>
- Raises
- RuleError
If some node from the list already exists in the rhs.
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inject_clone_node(self, n, new_node_id=None)[source]¶ Inject cloning of a node by the rule.
This procedure clones n in the preserved part and the right-hand side.
- Parameters
- nhashable
Node from lhs to clone
- new_node_idhashable
Id for the clone
- Returns
- p_new_node_idhashable
Id of the new clone node in the preserved part
- rhs_new_node_idhashable
Id of the new clone node in the right-hand side
- Raises
- RuleError
If the node to clone is already being removed by the rule or if node with the specified clone id already exists in p.
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inject_merge_nodes(self, node_list, node_id=None)[source]¶ Inject merge of a collection of nodes by the rule.
- Parameters
- node_listiterable
Collection of ids of nodes from the preserved part.
- node_idhashable
Id of the new node corresponding to the result of merge.
- Returns
- new_namehashable
Id of the new node corresponding to the result of merge.
- Raises
- RuleError
If a node with some id specified in node_list does not exist in the preserved part of the rule.
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inject_remove_edge(self, n1, n2)[source]¶ Inject removal of an edge by the rule.
- Parameters
- n1hashable
Id of an edge’s source node in p.
- n2hashable
Id of an edge’s target node in p.
- Raises
- RuleError
If some of the nodes are not found in p, or if a corresponding edge in p does not exist.
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inject_remove_edge_attrs(self, n1, n2, attrs)[source]¶ Inject a removal of edge attrs by the rule.
- Parameters
- n1hashable
Id of an edge’s source node in p.
- n2hashable
Id of an edge’s target node in p.
- attrsdict
Dictionary with attributes to remove.
- Raises
- RuleError
If edge n1-> n2 does not exist in the preserved part of the rule, or when the node whose attrs should be removed is itself is being removed by the rule.
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inject_remove_node(self, p_node_id)[source]¶ Inject a new node removal to the rule.
This method removes the indicated node from p
- Parameters
- p_node_id
Id of the node in p that should be removed by the rule.
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inject_remove_node_attrs(self, n, attrs)[source]¶ Inject a removal of node attrs by the rule.
- Parameters
- nhashable
Id of a node whose attrs to remove (node from the preserved part).
- attrsdict
Dictionary with attributes to remove.
- Raises
- RuleError
If n does not exist in the preserved part of the rule, or when the node whose attrs should be removed is itself is being removed by the rule.
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inject_update_node_attrs(self, n, attrs)[source]¶ Inject an update of node attrs by the rule.
- Parameters
- nhashable
Id of a node from the left-hand side whose attrs should be updated
- attrsdict
Dictionary of new attrs that will replace the old ones
- Raises
- RuleError
If node n does not exist in the left-hand side or is being removed by the rule.
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is_relaxing(self)[source]¶ Check if the rule is relaxing.
Rule is relaxing if it adds nodes/edges/attributes or merges nodes.
- Returns
- True if the rule is relaxing, False otherwise
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is_restrictive(self)[source]¶ Check if the rule is restrictive.
Rule is restictive if it removes nodes/edges/attributes or clones nodes.
- Returns
- True if the rule is restrictive, False
- otherwise
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merged_nodes(self)[source]¶ Get nodes merged by the rule.
- Returns
- nodesdict
Dictionary where keys are nodes from rhs and values are sets of nodes from p that are merged.
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removed_edge_attrs(self)[source]¶ Get edge attributes removed by the rule.
- Returns
- attrsdict
Dictionary where keys are edges from p and values are attribute dictionaries to remove.
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removed_edges(self)[source]¶ Get edges removed by the rule.
- Returns
- edgesset
Set of edges from lhs removed by the rule.
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removed_node_attrs(self)[source]¶ Get node attributes removed by the rule.
- Returns
- attrsdict
Dictionary where keys are nodes from p and values are attribute dictionaries to remove.
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removed_nodes(self)[source]¶ Get nodes removed by the rule.
- Returns
- nodesset
Set of nodes from lhs removed by the rule.
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to_commands(self)[source]¶ Convert the rule to a list of commands.
This method produces a list of commands corresponding to the rule. These commands follow a simple grammar of transformations that can be recognized by regraph.parser module.
- Returns
- commandsstr
Commands representing primitive transformations on the the lhs that are preformed in the rule.
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regraph.rules.compose_rule_hierarchies(rule_hierarchy1, lhs_instances1, rhs_instances1, rule_hierarchy2, lhs_instances2, rhs_instances2)[source]¶ Compose two rule hierarchies.