SMC Browser

Explore the Component Metadata Framework

In CMD, metadata schemas are defined by profiles that are constructed out of reusable components - collections of metadata fields. The components can contain other components, and they can be reused in multiple profiles. Furthermore, every CMD element (metadata field) refers via a PID to a data category to indicate unambiguously how the content of the field in a metadata description should be interpreted (Broeder et al., 2010).

Thus, every profile can be expressed as a tree, with the profile component as the root node, the used components as intermediate nodes and elements or data categories as leaf nodes, parent-child relationship being defined by the inclusion (componentA -includes-> componentB) or referencing (elementA -refersTo-> datcat1).The reuse of components in multiple profiles and especially also the referencing of the same data categories in multiple CMD elements leads to a blending of the individual profile trees into a graph (acyclic directed, but not necessarily connected).

SMC Browser visualizes this graph structure in an interactive fashion. You can have a look at the examples for inspiration.

It is implemented on top of wonderful js-library d3, the code checked in clarin-svn (and needs refactoring). There is also some preliminary technical documentation

See also SMC on CCV for more general and theoretical information about the SMC module and the SMC Browser.


The graph is constructed from all profiles defined in the Component Registry. To resolve name and description of data categories referenced in the CMD elements definitions of all (public) data categories from DublinCore and ISOcat (from the Metadata Profile [RDF] - retrieving takes some time!) are fetched. However only data categories used in CMD will get part of the graph. Here is a quantitative summary of the dataset.

Multiple variants of the graph are being offered:

SMC graph basic
the basic graph contains profiles -> components -> elements -> datcats; processing 155 profiles yields a graph with over 4.500 nodes and over 7.500 edges
SMC graph all
additionally rendering the profile-groups and relations between data categories (from Relation Registry)
only profiles + datcats
just profiles and data categories are rendered (with direct links between those, skipping all components and elements)
profiles + datcats + datcats + groups + rr
as above but again with profile-groups and relations
profiles similarity
just profiles with links between them representing the degree of similarity based on the reuse of components and data categories

When inspecting the numbers, it is important to be aware of the occurrence expansion resulting from the reusability of the components. So in an example, a component C has 2 subcomponents and is reused within one profile by two other components A and B, the resulting profile will consist of (at least) 8 components ([A, B, A/C, B/C, A/C/C1, A/C/C2, B/C/C1, B/C/C2]), although only 5 distinct components are used. The same goes for elements in reused components. In most cases it is indicated in the label, if the number reflect distinct items, or all (expanded) occurrences.

(Some of the) numbers in the statistics lead to a list of corresponding terms. E.g. in the summary for a profile, clicking on the components-number lists all the components of given profile alphabetically. Currently there are such lists for:

  • profile -> components
  • profile -> elements
  • profile -> data categories
  • data category -> profiles

User Interface

The user interface is divided into 4 main parts:

Lists all available Profiles, Components, Elements and used Data Categories The lists can be filtered (enter search pattern in the input box at the top of the index-pane). By clicking on individual items, they are added to the selected nodes and get rendered in the graph pane.
Main (Graph)
Pane for rendering the graph.
This is the control panel governing the rendering of the graph. See below for available Options.
In this pane, overall summary of the data is displayed by default, but mainly the detail information about the selected nodes is listed here.


Following data sets are distinguished with respect to the user interaction:

all data
the full graph with all profiles, components, elements and data categories and links between them. Currently this amounts to roughly 4.600 nodes and 7.500 links.
selected nodes
nodes explicitely selected by the user (see below how to select nodes).
data to show

the subset of data that shall be displayed.

Starting from the selected nodes, connected nodes (and connecting edges) are determined based on the options (depth-before, depth-after).

The nodes are colour-coded by type:

the legend to the graph

There are multiple ways to select/unselect nodes:

select from index

by clicking individual items in the index list, the item will be added to the selected nodes

clicking on an already selected item unselects it

select in graph

by clicking on a visible node in the graph, the node will be added to the selected nodes

clicking on an already selected node unselects it

select area in graph
by dragging (hold mouse button down and pull) a rectangle in the graph pane, all nodes within that rectangle get selected all other nodes will be unselected
unselect in detail pane
clicking on an item in the detail pane unselects it
select in statistics
as mentioned in Data (some) numbers in the statistics reveal a list of corresponding terms. Clicking on these terms in the statistics page leads to the browser, with given term as selected node (and default settings)
select in statistics in the detail pane
the numbers from statistics page are shown also in the detail pane for selected nodes. Here, clicking on a term from these lists adds it to the graph, as a selected node.
on mouse over a node, all connected nodes to given node (and connecting links) within the visible sub-graph are highlighted and all other nodes and links are faded
drag a node
click and hold on a node, one can move the node around, however usually the layout is stronger and puts the node back to its original position. Not so with the freeze-layout, that freezes all the nodes and lets you move them around freely


The navigation pane provides the following options to control the rendering of the graph:

select data source
how many levels of connected ancestor nodes shall be displayed
how many levels of connected descendant nodes shall be displayed
approximate distance between individual nodes (not exact, because it is just one of multiple factor for the layouting of the graph)
the higher the charge, the more the nodes tend to drift apart
factor for "cooling down" the layout, lower numbers (50-70) stabilize the graph more quickly, but it may be too early, with higher numbers (95-100) the layout has more time/freedom to arrange, but may get jittery

N = all nodes have given diameter N;

usage = node is scaled based on how often the node appears in the complete dataset i.e. often reused elements (like description or language) will be bigger

show/hide all labels hiding the labels accelerates the rendering significantly, which may be an issue if more nodes are displayed. irrespective of this option, on hover labels for all and only the highlighted nodes are displayed
straight or arc (better visibility), arrow or line

There are a few layouting algorithms provided. They are all not optimal in any way, but most of the time, they deliver quite good results. For different data displayed other algorithm may be more appropriate:

undirected layout, trying to spread the nodes in the pane optimally, equally in all directions This is the underlying layouting algorithm. All the other layouts build on top of it, by just adding further constraints.
top-down layout respect the direction of the edges, children are always below the parents
left-right layout respect the direction of the edges, children are always right to the parents (at least they should be, currently, in certain configurations, the layout does not get the orientation for some links right)
a layout that "tends" towards left to right arrangement, but not strictly so (experimental)
strict left to right reusing the x-positioning as determined by dot Arranges the nodes in strict ranks (typical for dot layout) This is done in a separate preprocessing step for the whole graph, so the positioning may be suboptimal for a given subgraph. The y-coordinate is approximated on the fly by the base algorithm.
this is actually a "no-layout" - the nodes just stay fixed in their last position, However, individual nodes still can be dragged around, so this can be used to adjust a few nodes for better legibility (or aesthetics), but only when you start moving around inividual nodes, you will learn to appreciate the great (and tedious) work of the layouting algorithms, so generally you want to try to play around with the other settings to achieve a satisfying result.

Linking, Export

The navigation pane exposes a link, that captures the exact current state of the interface (just the options and the selection, not the positioning of the elements), so that it can be bookmarked, emailed etc.

Furthermore, there is the download, that allows to export the current graph as SVG. This is accomplished without a round trip to the server, with a javascript trick serializing the svg as base64-data into the url (so you don't want to save (or see) the exported url). But you can both, right click the link and [Save link as...], or click on the link, which opens the SVG in a new tab where you can view, resize, print and save it. Employing this simple method also means, that there is no possibility to export the graph in PNG, PDF or any other format, because this would require server-side processing. (However this is a planned future enhancement.)


Chrome is by far the fastest, followed by IE(9). A serious performance degradation was observed for graphs above 200 nodes on Firefox. Showing labels also significantly affects performance.
When the graph gets to big, it does not fit in the viewing pane. This will be tackled soon (either scrollbars or applying boundaries). Meanwhile, you can reduce the link-distance and charge parameters or change the layout.

Plans and ToDos

Substantial issues:

Smaller enhancements of the user interface: