MarkLogic

Fig 02 - MarkLogic Data Hub components

Figure 2 provides a more detailed view of how MarkLogic Data Hub works. However, some of this may take some explanation, especially with respect to data integration processes. In MarkLogic this is model-driven. That is, instead of building a one-to-one pipeline you build a source to model mapping and a model to target mapping. Imagine that you have 100 sources which might map to any of 10 targets. If you use a traditional point-to-point approach you need 1,000 pipelines. If you use a model-driven approach you need 110. The immediate benefits deriving from this approach are obvious: far less development and maintenance, as well as logical separation between the sources and targets. You can change a mapping, and test it, without interrupting existing processes. There are check-in and version control features to support updated mappings.

However, there are also less obvious benefits. What you are actually creating during this process is an entity model, or series of entity models, which represents an abstraction layer between source and targets, with semantic models that are persisted within the underlying database. This allows curation of that model, both in terms of data quality and, because of the semantic nature of models, support functions like classification and metadata management (including data lineage). In effect, it offers much the same capabilities as a data catalogue with the exception that you cannot automatically crawl data sources to create the catalogue. On the other hand, the underlying multi-model (graph) database allows you to construct a knowledge graph through which you can explore all the relationships that exist between different data elements. This is done through the Data Hub Central user interface, which provides a no/low-code environment targeted at domain experts rather than IT folk. In addition to allowing you to explore your data catalogue equivalent via a search interface it is also extensible, allowing you to define plug-ins for, say, extra data quality functions that are not provided out of the box. Automation and machine learning are implemented in various places across the Data Hub.

From a data integration perspective, MarkLogic refers to consumption models rather than targets. This is because the environment is by no means tied to populating data warehouses and data lakes but also supports direct feeds into business intelligence tools, machine learning platforms and applications.

More generally, MarkLogic Data Hub acts as a hub for data management on top of MarkLogic Server. This means that it inherits the latter’s multi-model approach, then exposes it via the unified data integration and management platform. It also offers a number of additional features, including data lineage tracking, fast data pipelines, and additional governance features. Most notably, it allows you to directly enforce policy rules on your queries at the code level, filtering the results in order to comply with the applied policy and thus embedding governance into the queries themselves. As a means of policy enforcement this is highly effective because it is present in your system at a deep level, which means it cannot be ignored or easily circumvented.

Finally, with respect to data privacy, GDPR-style permissions can be attached to models during the curation phases, and both redaction and anonymisation (data masking) are supported.

As a concept, the idea of putting an abstraction layer between sources and targets is a strong one. And implementing that on top of a multi-model database that supports a graph model provides powerful support for other data management functions. It is also worth commenting on the company’s pricing model. This is consumption-based. Moreover, the Data Hub Service is serverless and separates storage from compute, with different compute functions (say, loading data as opposed to curation processes) also separated. This is taken into account for pricing purposes, so it is as efficient as it possibly can be.

The Bottom Line

We are impressed with MarkLogic Data Hub. MarkLogic is less well known outside of its core markets but its innovation, and the agility of its solution mean that it should be considered a leading vendor.

MarkLogic Server serves as the storage layer for MarkLogic Data Hub. As a multi-model database, it can be used to store documents (including JSON, XML and flat text documents), relational data via tables, rows and columns, and graph data via RDF triples (although technically it uses quads – which means it supports named graphs. The database is ACID compliant with immediate consistency, and there are enterprise grade features available such as high availability, resilience and so forth. Security capabilities are also provided, including encryption and key management, role-based security, redaction and even data masking. As far as graph is concerned, it supports inferencing via backward chaining, and there are built-in semantic search capabilities as well as (bi-)temporal and geospatial functionality.

Appropriate query support is provided for each model: search for documents, SQL for relational data, and SPARQL for graph data. The latter also supports GraphQL and GeoSPARQL. MarkLogic also provides its Optic API for multi-model querying using a combination of the aforementioned query languages. Notably, relational and graph data in MarkLogic Server leverage the same index technology, meaning that you can query the same data as either a set of triples or as rows and columns. All queries are composable between types of model, and consistency is maintained across all models that represent the same data.

You can also leverage multiple models simultaneously. For example – in fact, this is a typical use case – you can use MarkLogic to build a knowledge graph where the entities are documents and the relationships are triples. Among other things, this means that the nodes in your graph can contain properties (read: metadata) in and of themselves, without requiring additional nodes in the graph. This allows you to store a wealth of property information within your graphs, and thus provide fodder for detailed searching and querying, without fear that the size of your graphs will balloon out of all reasonable proportion.

Alternatively (or additionally), you can annotate your documents using triples or embed your triples inside of your documents. By partitioning your set of triples between your documents, you can leverage document search to rapidly locate which documents – and therefore which subset of your triples – are relevant to your query, then apply your query strictly to that subset. This has benefits for speed and scalability.

Fig 02 - MarkLogic Data Hub QuickStart

As far as the MarkLogic Data Hub itself is concerned, it acts as a hub for data management on top of MarkLogic Server. This means that it inherits the latter’s multi-model approach, then exposes it via a unified data integration and management platform. It also offers a number of additional features, including data lineage tracking, fast data pipelines, a “QuickStart” user interface (see Figure 2), and additional governance features. Most notably, it allows you to directly enforce policy rules on your queries at the code level, filtering the results in order to comply with the applied policy and thus embedding governance into the queries themselves. As a means of policy enforcement this is highly effective because it is present in your system at a deep level, which means it cannot be ignored or easily circumvented.

MarkLogic Server’s greatest selling point is undoubtedly the data agility that users get because it is multi-model and has schema flexibility. Being able to leverage graph, relational and document data interchangeably allows you to choose the right tool for the right job, and moreover, leveraging them in combination can create a solution that is more than the sum of its parts. Leveraging documents inside of graphs, and triples inside of documents, are particularly strong examples of this. The latter enables MarkLogic’s query optimisation, while the former allows you to store much more property information in your graph than would normally be practical. Moreover, the document format allows you to store information as needed, without regard for whether it fits into a rigid schema. This enables you to retain all relevant information, and thus provide a complete business context and provenance for each of the data assets within your (knowledge) graph.

MarkLogic Data Hub adds to this by providing a window into your multi-model data. It gives you multiple lenses with which to view your data (notably, relational and graph) and in general acts as a unified platform for interacting with and curating your graph, relational and document data. Its unique (and, as already indicated, highly effective) approach to policy management – which could more appropriately be described as policy enforcement – is worth noting as well.

The Bottom Line

MarkLogic Server excels as a multi-model database not only because it gives you an expanded range of options for storing data, but because it provides ways for those options to interoperate, and thereby produce synergies that would otherwise not be possible. MarkLogic Data Hub builds on this foundation by providing fast ingestion, curation, and data access. In short, if you want to leverage graph, relational and document data together, you should be looking at MarkLogic.