message: Ref relations by constants
diff: * limitations under the License.
  */
  -import { Entity } from '@backstage/catalog-model';
  +import {
  + Entity,
  + RELATION_PROVIDES_API,
  + RELATION_PART_OF,
  +} from '@backstage/catalog-model';
  import { catalogApiRef } from '@backstage/plugin-catalog-react';
  import {
  DependencyGraph,
  @@ -81,14 +85,14 @@ export function SystemDiagram({ entity }: SystemDiagramProps) {
  if (catalogItem.relations) {
  for (const relation of catalogItem.relations) {
  switch (relation.type) {
  - case 'providesApi':
  + case RELATION_PROVIDES_API:
  systemEdges.push({
  to: `${catalogItem.kind}:${catalogItem.metadata.name}`.toLowerCase(),
  from: `${relation.target.kind}:${relation.target.name}`.toLowerCase(),
  label: 'provides API',
  });
  break;
  - case 'partOf':
  + case RELATION_PART_OF:
  systemEdges.push({
  from: `${catalogItem.kind}:${catalogItem.metadata.name}`.toLowerCase(),
  to: `${relation.target.kind}:${relation.target.name}`.toLowerCase(),
  