Problems generating or using empty HDT files about hdt-java

[D063520]

this seams to work in the current version

@mielvds can you check on your side?

[D063520]

In fact inside the java version everything is working .... but it is not compatible with the C++ version. Empty file created with the c++ version

empty file created with the java version:

[D063520]

So for the direction

1. compressing an empty HDT file with c++
2. opening the hdt file with java version
   my guess is that the c++ version is wrong. Here:

hdt-java/hdt-java-core/src/main/java/org/rdfhdt/hdt/triples/impl/BitmapTriples.java

Line 214 in 594e5f6

adjY = new AdjacencyList(seqY, bitmapY);

the seqY has length zero but bitmapY has length 1. I'm 90% sure this is encoded in the HDT file wrongly.

Why then it opens in c++ and not in java? The c++ version is not making the same check as java

https://github.com/rdfhdt/hdt-cpp/blob/332a9cc2d5273e76b9daad366f7d2f80adb6b3fc/libhdt/src/sequence/AdjacencyList.cpp#L38

hdt-java/hdt-java-core/src/main/java/org/rdfhdt/hdt/compact/bitmap/AdjacencyList.java

Line 49 in 594e5f6

if (array.getNumberOfElements() != bitmap.getNumBits()) {

that is why in c++ we can search over it and not in java.

Moreover if we remove the check in java we can open the file and it contains no triples.

@mielvds : should I open an issue in the c++ version?

[D063520]

For the direction:

1. compressing an empty HDT file with java
2. opening the hdt file with c++ version

I think the best is to debug it in the c++ version.
@mielvds I would move this also to the c++ version therefore .....

[mielvds]

Nice findings @D063520 ! Yes, let's bounce this over to the C++ version. and close this issue

[D063520]

Ok, I'm moving the first issue ....