I saw that in Finnish law, one can make a few copies for his own use. Suppose that a junior programmer downloads a dataset for his own use from legal source. But then he makes a mistake in programming and program makes several copies of the data to his computer memory. Has the programmer made an illegal copy of the data?
If the programmer has permission to download the dataset then he is doing so under some kind of license. That license will specify the terms of what is permissible.
The Finnish copyright law includes a specific term for databases:
(4) Whoever has a right to use a database may make copies of it and perform all other acts necessary for accessing the database and for normal use of its contents. (250/1998)
So the programmer can create as many copies on his own computer as he likes.