Modelling principles

Django and sub-classing (#54 – #56)

By |2017-11-14T17:17:57+11:00October 17th, 2017|Django, Modelling principles, Newsletter|

When modelling data, we often need to distinguish between different types of objects.  For example, a mapping application may need to store information about both roads and lakes, or a library catalogue may need to store data about both books and DVDs.  With these examples, the objects can be quite diverse and the details stored [...]

Hardware hides performance pitfalls (#52)

By |2018-10-21T00:09:16+11:00September 21st, 2017|Modelling principles, Newsletter|

Data modelling is not the only limiter of performance. When I first started working with databases, performance in all aspects of computing was much worse than it is now.  However well an expert might craft a query, and however simple the query might be, technical restrictions would always limit the performance to just a few [...]

Missing data (#51)

By |2018-10-21T00:11:57+11:00September 11th, 2017|Modelling principles, Newsletter|

A very common problem with databases is missing data. Missing data makes searches difficult (or impossible) and statistics unreliable. Two common reasons for this are: Records contain optional fields which have been left empty. Records are completely missing because some of the mandatory information was not available. Since the missing data was in mandatory columns, [...]

Which RDBMS? (#50)

By |2018-10-21T00:16:30+11:00September 4th, 2017|Modelling principles, Newsletter|

In this series of newsletters, we concentrate on data modelling in general and discuss relational databases when we need to consider specific applications.  In general, we do not consider the so-called “NoSQL” databases.  Relational database management systems lend themselves to the use of fixed schemas and also provide easy type checking. […]

Importing data (#49)

By |2018-10-21T00:20:49+11:00August 28th, 2017|Modelling principles, Newsletter|

Often the data we are modelling must be imported into a database.  Data importing can be a complex and difficult task. Often the data must come from several different sources and the importing will occur in several steps. Sometimes the data for different tables can come from different sources and must be imported at different [...]

Performance (#48)

By |2018-10-21T00:27:01+11:00August 21st, 2017|Modelling principles, Newsletter|

In a database, good performance is vital. So, how can we be sure we will have good performance in a project?  What will make a data model good for performance or bad? And what is good performance anyway? Let’s start by defining good performance. […]

Use case design (#46)

By |2018-10-20T22:35:42+11:00August 1st, 2017|Modelling principles, Newsletter|

Use cases must be designed in cooperation with future users of the software or database.  Designers will have a theoretical view to some extent, while users have more practical demands.  Theoretical matters are not an end in themselves, so aim for practical solutions. […]

What do we need? (#45)

By |2018-10-20T23:07:34+11:00July 24th, 2017|Modelling principles, Newsletter|

If you are going on a long hike; planning an overseas trip; building a new house; planting a garden; or doing many other things in life, one of the main questions is “What do I need?” Sometimes it is deciding what we need to take with us, while at other times it is deciding what [...]

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