Numerical Algorithms: Variational Integrators

When I was rummaging through my digital attic I found code that I had worked on a few years ago. It is not related to data or database technologies but it is in itself interesting, so that I thought I’d better share it.

To calculate integrals in mathematics or solve differential equations in physics or chemistry you often need a computer’s help. Only in very rare cases can you express the integral symbolically. In most instances you have to be satisfied with a numerical solution, which for many problems is perfectly fine.

read on...

How to Multiply Across a Hierarchy in Oracle: Performance (Part 2/2)

In the first part I have shown several options to calculate aggregation functions along various branches of a hierarchy, where the values of a particular row depend on the values of its predecessors, specifically the current row’s value is the product of the values of its predecessors.

Performance was the elephant in the room. So, it’s time to take a look at the relative performance of the various alternatives presented.

read on...

How to Multiply Across a Hierarchy in Oracle: SQL Statements (Part 1/2)

Hierarchical and recursive queries pop up from time to time in the life of a database developer. Complex hierarchies are often best handled by databases that are dedicated to such structures, such as Neo4j, a popular graph database. Most relational database management systems can generally deal with reasonable amounts of hierarchical data too. The classical example of hierarchical queries in SQL is the employees table: construct the organization chart with the CEO sitting at the top of the tree and all employees dangling from the branches on which their respective managers have placed their bottoms. While a direct acyclic graph of all company talent may tickle your fancy, I very much doubt it.

read on...

Homelessness: A Problem with Data but Few Solutions

A while ago I had the pleasure to visit Strasbourg, the capital of the Alsace region and home of the European parliament. Strasbourg is a lovely city to spend a few days, go shopping, enjoy French and Alsatian cuisine, and take in the scenery, most notably the picturesque Petite France area with its half-timbered houses and restaurants serving local delicacies along the river Ill.

The story I want to tell has very little to do with Strasbourg though. It is about homelessness, statistics on homelessness, and more to the point: the lack of action by our governments to solve the problem of homelessness.

read on...

The Data-Quality Doctor

When it comes to data quality, many companies are still stuck in firefighting mode: whenever a problem arises, a quick fix is introduced, often without proper documentation, after which the problem is filed under ‘H’ for “hopefully not my problem the next time around”. The patches are often temporary, haphazard, and cause more problems downstream than they really solve. In most instances there is no obvious reason for it, which makes a bad situation worse. It reminds me of the saying that the treatment is worse than the disease, so it’s time to bring in the doctor…

read on...