The Computational Materials Repository

3.3 System Components and Processes 71victims machine when the file is opened.) The goal could be to get passwords,modify or delete content, install a virus, et cetera. In Python all functions thatinteract with the operating system or allow dynamic code execution (e.g. exec,eval, os.system, os.popen, execfile, input, compile) should not be used with datafrom the third-party input files. The only function that CMR uses when parsingthe third-party file is eval. This function is used to convert strings to numbers orarrays. Although potentially dangerous it is easy to sanitize eval by manually setthe local global environment as unavailable. This prevents eval from executingany code. The small code below demonstrates the effect: first the dangerousversion and then the sanitized one.# dangerouse v a l (” open ( ’ / tmp/new ’ , ’w ’ ) . w r i t e ( ’ a l e r t ’ ) ” )# s a n i t i z e de v a l (” open ( ’ / tmp/new ’ , ’w ’ ) . w r i t e ( ’ a l e r t ’ ) ” , { ’ b u i l t i n s ’ : None } , {})For more information about eval and python in general see [17].3.3.3.3 SchemasThere are two kinds of schemas: the CMR schema and the XML schema.(The database schema is of different nature and discussed in section 3.3.2.3.)The CMR schema is the main schema and defines for every calculator (andcalculator version) the fields, their types and units, if available. The XMLschema is derived from the CMR schema and used in order to perform the db-filevalidation (3.3.4.3).Purpose: The CMR schema is the description of the data in the db-file and isused during the extraction and during the validation.Implementation: The CMR schema is implemented in Python and defines allvariables stored in the corresponding db-file. Fig. 3.8 shows an extract of theGPAW schema. These CMR schemas can be adapted to specific program versionsor they can be designed loose to accept several versions with the same schema.It is also possible to derive a schema from another one and make it specific for acertain type of calculation. One could imagine to make one for a chemisorptioncalculation where the atoms in the surface have to be put as separate fields.Example: section 2.9.33.3.4 Processes3.3.4.1 Conversion to /writing of a db-fileThe conversion process takes an original output file and converts it to a db-file.Purpose: Create db-files and define keywords/fields and attach scripts/files.Usage: The creation of the db-files is performed by the user with the CLI(3.3.1.1)or with the cmr Python package.Process: First the file type is detected and the correct converter determined. Theconverter is responsible to select the correct version of the CMR schema (3.3.3.3)depending on the version of the input file. When the data is read from the