Category: Graph

Niko Neugebauer looks at a few additions to SQL Server graph support:

Now, in the next step we shall create a derived view, which shall contain the list with all Persons and Businesses, joining them together:

CREATE OR ALTER VIEW dbo.Followers AS 
	SELECT PersonId as Id, FullName
		FROM dbo.Person
	UNION ALL
	SELECT BusinessId, BusinessName
		FROM dbo.Business;

Now, the real new thing is that we can use such derived tables in SQL Server 2019 CTP 2.1 and Azure SQL Database together with the MATCH clause, in the statements such as the one below where we list all the followers of the “Real Stuff” company:

SELECT Followers.ID, Followers.FullName
	FROM Followers, Follows, Company
	WHERE MATCH(Followers-(Follows)->Company)
		AND CompanyName = 'Real Stuff'

This query works fine, delivering us the expected results while generating a pretty complex execution plan in the background.

Niko focuses on heterogeneous nodes and edges, as well as derived views.

Shreya Verma shows examples of using views and derived tables in SQL Server 2019’s graph database functionality:

We will be further expanding the graph database capabilities with several new features. In this blog we will discuss one of those features that is now available for public preview in Azure SQL Database and SQL Server 2019 CTP2.1: use of derived tables and views on graph tables in MATCH queries.

Graph queries on Azure SQL Database now support using view and derived table aliases in the MATCH syntax. To use these aliases in MATCH, the views and derived tables must be created either on a node or edge table which may or may not have some filters on it or a set of node or edge tables combined together using the UNION ALL operator. The ability to use derived table and view aliases in MATCH queries, could be very useful in scenarios where you are looking to query heterogeneous entities or heterogeneous connections between two or more entities in your graph.

It’s good to see the product team expand on what they released in 2017, getting the graph product closer to production-quality.

Shreya Verma announces one of the new additions to graph database support in SQL Server 2019:

SQL Server 2017 and Azure SQL Database introduced native graph database capabilities used to model many-to-many relationships. The first implementation of SQL Graph introduced support for nodes to represent entities, edges to represent relationships and a new MATCH predicate to support graph pattern matching and traversal.

We will be further expanding the graph database capabilities with several new features. In this blog we will discuss one of these features that is now available for public preview in SQL Server 2019, Edge Constraints on Graph Edge Tables.

In the first release of SQL Graph, an edge could connect any node to any other node in the database. With Edge Constraints users can enforce specific semantics on the edge tables. The constraints also help in maintaining data integrity. This post describes how you can create and use edge constraints in a graph database. We will use the following  graph schema created in the WideWorldImporters database for the samples discussed here.

I know that SQL Server 2017 was a bit underwhelming for graph database work, so I will be interested in seeing how much of the gap they cover in this release.

Adrian Colyer reviews a paper on the mathematical properties behind GraphQL:

The authors study the computational complexity of GraphQL looking at three central questions:

1. The evaluation problem: what can we say about the complexity of GraphQL query evaluation?
2. The enumeration problem: how efficiently can we enumerate the results of a query in practice?
3. The response size problem: how large can responses get, and what can we do to avoid obtaining overly large response objects?

In order to do this, they need to find some solid ground to use for reasoning. So the starting point is a formalisation of the semantics of GraphQL.

This is a review of a published academic paper rather than a how-to guide, so it’s math-heavy.  I am enjoying seeing the development of normal forms for graph processing languages—it’s the beginning of a new generation of normalization purists.

Amy Hodler gives us a quick summary of fifteen separate algorithms for traversing a graph in Neo4j:

6. PageRank

What it does: Estimates a current node’s importance from its linked neighbors and then again from their neighbors. A node’s rank is derived from the number and quality of its transitive links to estimate influence. Although popularized by Google, it’s widely recognized as a way of detecting influential nodes in any network.

How it’s used: PageRank is used in quite a few ways to estimate importance and influence. It’s used to suggest Twitter accounts to follow and for general sentiment analysis.

PageRank is also used in machine learning to identify the most influential features for extraction. In biology, it’s been used to identify which species extinctions within a food web would lead to biggest chain reaction of species death.

If you are interested in getting into graph databases, it’s useful to know these algorithms.