In many cases, CloverDX is able to detect metadata on edges automatically via metadata propagation. Metadata propagation is a process which propagates metadata through the graph based on a set of rules. The metadata to propagate is taken from sources such as edges with manually assigned metadata and from components that can inject metadata into the graph.

Figure 31.1.  Metadata propagation: metadata is propagated from the first edge on the left side to all connected edges.

You do not have to assign metadata manually to each edge in graph as metadata is propagated by default. You can override metadata on edges by manually selecting propagated metadata or by user-defined metadata.

Figure 31.2. Changing auto-propagated metadata to user-defined.

Figure 31.3. Changing user-defined metadata to auto-propagated.

Principles of Propagation

Metadata propagation depends on a graph layout, priorities of metadata propagation of particular component and manually assigned metadata. Metadata is propagated through directly or indirectly connected components and edges. To propagate metadata to an edge in a separated part of graph, an action from the user is needed.

Components may have different priorities of metadata propagation from both sides or can propagate one way only (e.g. Reformat).

Figure 31.4. Different priorities of metadata propagation

At least some metadata must be known: assigned by the user or propagated from a template on a port of a component.

An edge can have explicitly assigned metadata of another edge of the graph. Both edges do not have to be connected through any other components and edges. The user has to define an edge from which the metadata is propagated.

Figure 31.12. Metadata propagated from an unconnected distant edge

Let us explain the figure above: the metadata orders assigned to the edge between FlatFileReader and Filter are propagated through Filter.

We need the same metadata to read records using CloverDataReader as CloverDataWriter uses; therefore, we define that the edge between CloverDataReader and ExtSort takes metadata (see the green symbol) from the edge (the blue symbol) between Filter and CloverDataWriter.

Assigning Explicitly Propagated Metadata

Right click the edge to which you need to assign metadata and choose Select Metadata → Select Metadata from Edge

The message informs you about activation of a selection tool.

The cursor has changed and the graph editor pane is now transparent.

Click the edge you need to take metadata from.

The metadata has been propagated. The blue symbol denotes the source edge of metadata, the green one denotes the target edge.

Auto-propagated metadata has lower priority than explicitly defined metadata. You are free to override metadata assigned to the edge with different metadata. The auto-propagated metadata can be overridden in the same way as assigning new metadata to the edge: either by dragging and dropping from outline or by right clicking on the edge and choosing Select Metadata or New metadata.

SQL query metadata can be propagated; however, editing is done in the editor for user defined metadata and any changes must be saved as a new non-SQL query metadata. This limitation also applies to editing SQL query metadata in Transformation editor output (e.g. Reformat).

Auto-propagated metadata work also with jobflow components.

Figure 31.13. Metadata propagated from the another edge

	COMPATIBILITY NOTICE
	Auto-propagated metadata is available since version 4.0.0. To propagate metadata, you must also open the context menu by right-clicking the edge, then selecting the Propagate metadata item. The metadata will be propagated until it reaches a component in which metadata can be changed (e.g. Reformat, Joiners, etc.).