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Graph algorithms run on a graph data model which is a projection of the Neo4j property graph data model. A graph projection can be seen as a view over the stored graph, containing only analytically relevant, potentially aggregated, topological and property information. Graph projections are stored entirely in-memory using compressed data structures optimized for topology and property lookup operations.

The graph catalog is a concept within the GDS library that allows managing multiple graph projections by name. Using its name, a created graph can be used many times in the analytical workflow. Named graphs can be created using either a Native projection or a Cypher projection. After usage, named graphs can be removed from the catalog to free up main memory.

Graphs can also be created when running an algorithm without placing them in the catalog. We refer to such graphs as anonymous graphs.

This chapter explains the available graph catalog operations.

A projected graph can be stored in the catalog under a user-defined name. Using that name, the graph can be referred to by any algorithm in the library. This allows multiple algorithms to use the same graph without having to re-create it on each algorithm run.

There are two variants of projecting a graph from the Neo4j database into main memory:

In this section, we will give brief examples on how to create a graph using either variant. For detailed information about the configuration of each variant, we refer to the dedicated sections.

In the following two examples we show how to create a graph called that contains nodes and relationships.

Create a graph using a native projection: 

We can also use Cypher to select the nodes and relationships to be projected into the in-memory graph.

Create a graph using a Cypher projection: 

After creating the graphs in the catalog, we can refer to them in algorithms by using their name.

Run Page Rank on one of our created graphs: 

Once we have created graphs in the catalog, we can list information about either all of them or a single graph using its name.

List information about all graphs in the catalog: 

List information about a named graph in the catalog: 

The and columns are primarily applicable to Native projection. The and columns are applicable only to Cypher projection and are for graphs created with Native projection.

The is more time-consuming to compute than the other return columns. It is however only computed when included in the subclause.

The consists of information about the nodes and relationships stored in the graph. For each node label, the schema maps the label to its property keys and their corresponding property types. Similarly, the schema maps the relationship types to their property keys and property types. The property type is either or .

The indicates when the graph was created in memory. The indicates when the graph was updated by an algorithm running in mode. The yields the number of bytes used in the Java Heap to store that graph. The is the same information in a human readable format.

List information about the degree distribution of a specific graph: 

We can check if a graph is stored in the catalog by looking up its name.

Check if a graph exists in the catalog: 

We can remove node properties from a named graph in the catalog. This is useful to free up main memory or to remove accidentally created node properties.

Remove multiple node properties from a named graph: 

The above example requires all given properties to be present on at least one node projection, and the properties will be removed from all such projections.

The procedure can be configured to remove just the properties for some specific node projections. In the following example, we ran an algorithm on a sub-graph and subsequently remove the newly created property.

Remove node properties of a specific node projection: 

When a list of projections that are not is specified, as in the example above, a different validation and execution is applied; It is then required that all projections have all of the given properties, and they will be removed from all of the projections.

If any of the given projections is , the procedure behaves like in the first example.

We can delete all relationships of a given type from a named graph in the catalog. This is useful to free up main memory or to remove accidentally created relationship types.

Delete all relationships of type T from a named graph: 

Once we have finished using the named graph we can remove it from the catalog to free up memory.

Remove a graph from the catalog: 

We can stream node properties stored in a named in-memory graph back to the user. This is useful if we ran multiple algorithms in mode and want to retrieve some or all of the results. This is similar to what the execution mode does, but allows more fine-grained control over the operations.

Stream multiple node properties: 

The above example requires all given properties to be present on at least one node projection, and the properties will be streamed for all such projections.

The procedure can be configured to stream just the properties for some specific node projections. In the following example, we ran an algorithm on a sub-graph and subsequently streamed the newly created property.

Stream node properties of a specific node projection: 

When a list of projections that are not is specified, as in the example above, a different validation and execution is applied. It is then required that all projections have all of the given properties, and they will be streamed for all of the projections.

If any of the given projections is , the procedure behaves like in the first example.

When streaming multiple node properties, the name of each property is included in the result. This adds with some overhead, as each property name must be repeated for each node in the result, but is necessary in order to distinguish properties. For streaming a single node property this is not necessary. streams a single node property from the in-memory graph, and omits the property name. The result has the format , , as is familiar from the streaming mode of many algorithm procedures.

Stream a single node property: 

We can stream relationship properties stored in a named in-memory graph back to the user. This is useful if we ran multiple algorithms in mode and want to retrieve some or all of the results. This is similar to what the execution mode does, but allows more fine-grained control over the operations.

Stream multiple relationship properties: 

The procedure can be configured to stream just the properties for some specific relationship projections. In the following example, we ran an algorithm on a sub-graph and subsequently streamed the newly created property.

Stream relationship properties of a specific relationship projection: 

When a list of projections that are not is specified, as in the example above, a different validation and execution is applied. It is then required that all projections have all of the given properties, and they will be streamed for all of the projections.

If any of the given projections is , the procedure behaves like in the first example.

When streaming multiple relationship properties, the name of the relationship type and of each property is included in the result. This adds with some overhead, as each type name and property name must be repeated for each relationship in the result, but is necessary in order to distinguish properties. For streaming a single relationship property, the property name can be left out. streams a single relationship property from the in-memory graph, and omits the property name. The result has the format , , , .

Stream a single relationship property: 

Similar to streaming properties stored in an in-memory graph it is also possible to write those back to Neo4j. This is similar to what the execution mode does, but allows more fine-grained control over the operations.

The properties to write are typically the values that were used when running algorithms. Properties that were added to the created graph at creation time will often already be present in the Neo4j database.

Write multiple node properties to Neo4j: 

The above example requires all given properties to be present on at least one node projection, and the properties will be written for all such projections.

The procedure can be configured to write just the properties for some specific node projections. In the following example, we ran an algorithm on a sub-graph and subsequently wrote the newly created property to Neo4j.

Write node properties of a specific node projection to Neo4j: 

When a list of projections that are not is specified, as in the example above, a different validation and execution is applied; It is then required that all projections have all of the given properties, and they will be written to Neo4j for all of the projections.

If any of the given projections is , the procedure behaves like in the first example.

We can write relationships stored in a named in-memory graph back to Neo4j. This can be used to write algorithm results (for example from Node Similarity) or relationships that have been aggregated during graph creation.

The relationships to write are specified by a relationship type. This can either be an element identifier used in a relationship projection during graph construction or the used in algorithms that create relationships.

Write relationships to Neo4j: 

By default, no relationship properties will be written. To write relationship properties, these have to be explicitly specified.

Write relationships and their properties to Neo4j: 

We can create new Neo4j databases from named in-memory graphs stored in the graph catalog. All nodes, relationships and properties present in an in-memory graph are written to a new Neo4j database. This includes data that has been projected in and data that has been added by running algorithms in mode. The newly created database will be stored in the Neo4j directory using a given database name.

The feature is useful in the following, exemplary scenarios:

Export a named graph to a new database in the Neo4j databases directory: 

The procedure yields information about the number of nodes, relationships and properties written.

The new database can be started using .

After running the procedure, we can start a new database and query the exported graph: 

Chances are, you set up a catalog when you first installed Luminar. The catalog contains all of the information about your files including metadata like ratings and labels as well as any edits you make with the tools.

Remember, the edits you make in Luminar are always non-destructive when you work with a library. This means you are not changing the actual files but rather capturing the instructions into a database. When you are ready to share or use the file elsewhere you’ll export the image and apply the edits.

By default, Luminar’s catalog is installed in your Pictures folder. This isn’t an issue as long as you don’t include the Catalog folder when adding images. Doing this will add all preview images of the catalog to the Gallery/library.

The contents of a catalog are stored inside a folder. If backing up or moving the catalog, be sure to take the entire folder.

Set these controls before you start cataloging on your Koha system.