This repository contains a grammar for FM 94 BUFR (Binary universal form for the representation of meteorological data). The specification of the FM 94 BUFR is maintained by WMO in the Manual on Codes.
A BUFR is a binary code to encode meteorological data. The BUFR consists of sections. The following picture illustrates the different sections and their content.
Section 3 "Data description section" is the blue print for Section 4 "Data section".
Section 3 consists of descriptors. A descriptor contains 3 parts: F (2 bits) X (6 bits) and Y (8 bits).
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F = 0 is the "element descriptor" which defines a single data item (temperature, pressure, humidity, ...) in Table B
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F = 1 is the "replication descriptor". In this case X indicates the number of descriptors to be repeated, and Y the total number of replications. For Y = O we call the descriptor "delayed replication descriptor" and the number of replications is encoded in the data section with the so called "delayed descriptor replication factor" e.g. 0 31 000, 0 31 001, ...
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F = 2 is the "operator descriptor". The operations are described in detail in Table C
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F = 3 is the "sequence descriptor". A sequence descriptor defines a list of element descriptors, replication descriptors, operator descriptors and/or sequence descriptors. Table D contains all "sequence descriptors".
For the construction of Section 3 with the 4 types of descriptors (element, replication, operator and sequence descriptor) described above certain rules apply. The rules are described in detail in the Manual on Codes starting at regulations 94.1 and following.
Looking from a different perspective the rules as a whole can be interpreted as a language. This language is a set of valid sentences, and sentences are composed of phrases and clauses. Hereby a sentence structure follows a grammar. In our case the descriptors represent the phrases and clauses. The following sequence of descriptors is a valid sentence: 3 10 014 2 22 000 2 36 000 1 01 103 0 31 031 0 01 031. The rules for applying and combining the descriptors are our grammar. Additional rules for the replication descriptors are implemented as listener pattern.
The following picture shows a railroad diagram for the parser rule “operator descriptor expr” 
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You can find all railroad diagrams of the BUFR grammar in the BUFR grammar.
A basic version of a BUFR grammar is available on here. The grammar is formulated in ANTLR. With the help of the grammar a BUFR template developer can now check her/his template for syntax errors. The BUFR specification is maintained by WMO as a human readable document while a machine readable grammar does not exists. Furthermore no reference implementation of the BUFR specification exists. Therefore a validation of a BUFR decoder/encoder or an BUFR against the specification isn’t easy. This step could be simplified with a grammar.
Note: You can find the grammar in BNF1-style convention for the Java programming language on Oracle website or in antlr-style on github 1 Backus-Naur-Form.
The project uses gradle as a build tool. The project comes with a gradle wrapper. In case you consider to create an own gradle wrapper please you a recent gradle version (5.x or higher) installation and keep in mind that JDK 13 requires a gradle version 6.x.
Requirements: You need a recent java installation (JDK 8 or higher)
javac -version
Clone this repository:
git clone https://github.com/mheene/bufr-grammar.git
or download it as a zip-archive
wget https://github.com/mheene/bufr-grammar/archive/master.zip
Build the project as a standalone jar:
cd bufr-grammar
./gradlew jar
The jar file contains all dependencies. You will find the jar in the directory /build/libs
Check the file 301003.txt with the BUFR grammar and the additional replication descriptor checks:
java -jar build/libs/counter-0.0.1.jar material/valid/301003.txt
Use ANTLRs test rig (grun) to check a file against the grammar and visualize the parse tree:
./gradlew grun -PinputFile=material/valid/301003.txt
Verify all WMO sequences (Table D) against the grammar (including additional replication descriptor checks) and some additional test cases.
./gradlew test
An motivation and introduction including examples to the BUFR grammar is available as a powerpoint talk. The poster is available as pdf and a powerpoint.