Storage of test measurement data in LabVIEW (6)

      To put it bluntly, this file format is a binary file. There are only two VIs, one for reading and one for writing. It basically supports any type of data in LabVIEW. As long as you can create data in LabVIEW, you can store it in this file format. It can be guessed that what these two VIs do is relatively simple. Just write the data in the memory of LabVIEW to the file. Of course, if you do this, the efficiency is also relatively high because there are no calculation steps. But there are also some disadvantages. For example, writing data directly to the file is not necessarily a good idea. The real problem is how to manage this data. For example, when reading a file, you also need to know what type of data these files store, where they are stored in the file, and so on.

      In general, if the user pursues pure file writing speed and does not care about whether there will be difficulties in reading the file in the future (in fact, if a file is only written and not read, it is meaningless), then it is still possible to use such a file format.

      Next, we will introduce the TDM file format.

      TDM files refer to files with the suffix .TDM. The logical storage model of the file follows NI's TDM Data Model , a three-layer structure. TDM files are mainly divided into two physical files, one is the main file with the suffix TDM, which stores raw data and attribute information; the other is the header file with the suffix TDX, which mainly stores attribute information for easy search, as an index file. The main file is similar to the XML structure, while the header file is a binary file. The reason is very simple: the header file is mainly used to index and search data, so it has a higher requirement for reading speed, so it is more suitable as a binary file.

      The operation of TDM files is mainly completed through Storage VIs in LabVIEW. I personally feel that the biggest advantage of the TDM file format is data management. The file formats introduced before did not give much consideration to data management. The TDM file format is divided into three structures and can add user-customized attributes, which is more convenient to use. Let's take a simple example: many people bring lunch at noon and put it in a lunch box. Ordinary files are a hodgepodge, with rice and vegetables mixed together, which is inconvenient to eat and looks messy; while TDM files are like lunch boxes with partitions, where rice and vegetables can be placed separately, which is convenient and tidy.

      With NI's progress in test and measurement files, the TDM file format has been gradually replaced by the TDMS file format. Next time, we will specifically introduce TDMS.