I don't want to make this into any kind of flame war or anything, but I must address a couple of points here. I do not know what Frank Kalis thinks about the models described as the article is mainly a description of them, so these comments are not made to say he is wrong, they are written to address some points in the article that I think can be wrongly understood or accepted by some readers.
As said in the article, the relational model clearly distinguishes the logical desgin from the physical. The relational model is all about the logical and nothing about the physical part. Therefore it is impossible to say that any other database management model has better or worse performance, because performance is based on the physical design solely. This is in fact the greatest advantage of the relational model, apart from it's theoretical foundation (which no other model has, or at least not as clear), that the decisions you make on logical design issues will not affect the physical design. It is up to the RDBMS to decide how the logical design you create is best handled physically.
For the same reasons, it is also not correct to say that "[the] most significant [of] several weaknesses of the relational model ... is the inability to handle BLOB's." In the relational model, a relation has one or more attributes that are defined as being of specific domains. There is nothing that says that a domain can not be a BLOB or any other type of data. For a complete discussion and description of this see for instance the paper 'What first normal form really means' by C.J Date. Any flaw in handling these domains is purely a fault of the DBMS, not the relational model. Here is a nice quote from the above mentioned paper:
A proper object/relational system is just a relational system with proper type support ... --which simply means it's a proper relational system, no more and no less.
Regarding the OO 'model':
"The developer of such a system is responsible for implementing methods and properties to handle the data in the database from within his object-oriented application. There is no longer a strict distinction between application and database."
I would say that there is no longer a database, or at least not a DBMS. The reason to have a DBMS is precisely to have a centralized system for controlling the database, especially the integrity of it, so that the application developers do not need to (or must not even) know and control how to access the data. Using this approach we regress back to 40 years ago and leave all the work to each application, and we can only hope that each application takes care of what needs to be taken care of. Also, this means that each database you create is heavily linked to a specific application, if you want some other application to access the same data in just a slightly different way you probably need to either make changes to the first application or make the integrity constraints even more complex than what is already necessary using this 'model'. You'll notice that I put the word model in quotes when discussing the OO 'model'. This is because I do not think it is a complete data model, unlike the relational model. See for instance 'Something to call one's own'.
Finally, I have to disagree with the conclusion that "there (still) is a world outside the relational model, which can be pretty exciting to discover". All of these other so-called models are either old ones that were replaced by the relational model because of the flaws they had, or regressions to these old models by re-inventing them and calling them something different. The relational model is based on set theory and predicate order logic, anything trying to replace the relational model must also be a replacement for these theories several centuries old and proven.
With all this said, I still find this a good and interesting article as it brings up the discussion of points like these, and I kind of think that is one of the reasons why Frank wrote it.