Decoupling Links 'R' Us components from the underlying data stores

Both the link-crawler component that we created in Chapter 7, Data-Processing Pipelines, and the PageRank calculator component that we built in Chapter 8, Graph-Based Data Processing, were designed to work with one of the data store implementations from Chapter 6, Building a Persistence Layer.

To this end, when configuring these components, we are expected to provide suitable concrete data store implementations that satisfy the graph.Graph and index.Indexer interfaces. If we were building a monolithic application, we would normally be performing this bit of initialization inside the main package, as follows:

1. Import the package with the data store drivers we want to use in our application (for example, the CockroachDB backed link-graph and the Elasticsearch backed text indexer).
2. Create new driver instances...