Implementation of a Tree Structure in LabVIEW

[John Lokanis]

Hi,

I have put together a set of VIs to store data in a tree structure within LabVIEW. This method uses variant attributes to build the tree. Insertion is slower than a direct write to an array of clusters would be but reading back data is very fast. The reason insertion is slow is due to the dataflow nature of LabVIEW. The Tree must be rebuilt with each write.

Take a look at the code and let me know if you find any bugs or improvements. This would be a good tool to implement with LabVOOP, but I have not yet dived into that subject so it will have to wait.

The basic idea of the structure is that a variant can have attributes that are name-value pairs. The name must be a string, but the value can be anything. It can even be another variant that has it's own set of attributes. This is what enables the tree to be built. I have implemented three functions: read, write and delete. Each one operates on a single node in the tree. The data input is a variant. If a node in the branch path does not exist when writing, it is automatically added. The tips of each branch are the only places where actual data is stored in the variant. All branching nodes only contain attributes describing their sub-branches.

The path to a tip node is described as an array of strings. Each element in the array is a node in the tree that leads to the tip where the data is stored.

I also included some code that adds the top level caller VI name to the top of the path. This allows you to use the structure across several VIs and keep the data separate. We use this in a system where we spawn many VIs from a single VIT and need to maintain "global" local data.

Storage of the tree is implemented as a LV2 Global.

I hope you find this useful. If I have reinvented someone else's wheel, please send me a link to their code so I can compare and learn.

-John

BTW: When building this I found a bug in LabVIEW 8.20. The Get Variant Attribute function has an input called 'default value' that is supposed to default to an empty variant if nothing is wired. In practice, this function actually defaults to the last found variant from previous calls. So, to get it to work as described in the help, you need to wire an empty variant into this input.

[Michael Aivaliotis]

Please submit to the code repository.

[TG]

QUOTE(Michael_Aivaliotis @ Feb 21 2007, 09:03 PM)

Please submit to the http://forums.lavag.org/downloads.html' target="_blank">code repository.

jlokanis

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Could you post that again

I think the LLB is corrupted somehow. I could not launch or load it.

Thanks

[John Lokanis]

I am attaching the .llb again. I made some edits and improvements as well. You can now write data to nodes in the middle of the tree and the branches will be maintained. I also optimised the code a bit more.

BTW: This is written in 8.20. I don't have a 7.1.1. system setup to downgrade the code to an older version. Sorry.