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Table of Contents

EVD and Data Types

EVD’ stands for ‘EVL Data Definition’ and it is the way how to specify structure of data sets in EVL. It can be used either inline, as a component option, or in an *.evd file.

EVL uses mostly standard C++ data types, so most of them are well known.

EVD Structure

Firstly an example of evd file, which defines data types for some csv file:

ID           int                sep=";"
Name         string             sep=";"  null=""
"Birth Date" date("%-d.%-m.%Y") sep=";"  null="1.1.1970"
Amount       decimal(12,3)      sep=";"    thousands_sep=","
"Created At" datetime           sep="\n" null="0000-00-00 00:00:00"

In general each nonempty line of EVD file looks like this:

<indent> Field_Name <blank> Data_Type <blank> EVD_Options



might be empty, 2 spaces, 4 spaces, 6 spaces, etc., to define a substructure of compound data types, see Compound Types for details,


is a sequence of any printable ASCII characters below 128. When a space is used, then whole field name must be quoted by double quotes. Special characters (also only ASCII ones under 128) must be escaped, e.g. ‘\n’, ‘\r’, ‘\t’, ‘\v’, ‘\b’, ‘\f’, ‘\a’, ‘\"’, ‘\\’, or in hexa ‘\x??’. Characters other than letters, numbers and underscore are replaced by underscore in mappings. All these field names are valid:

                            // Name in mapping:
recommended_field_name      // recommended_field_name
"Field with a Space"        // Field_with_a_Space
'field-with-a-hyphen'       // _field_with_a_hyphen_
"$field_with_dollar"        // _field_with_dollar
'single_quoted'field'       // _single_quoted_field_
"with\nnewline"             // with_newline

is one of:


is <blank> separated list of options, see EVD Options


is one or more spaces and/or tabs.


Standard C-style comments can be used in evd file, for example:

street_id    int
street_name  string
street_code  string  null=""  // but NOT NULL in DB
/* COMBAK: street_code will be replaced by street_num later this year
street_num   long

Inline EVD

For the most of the EVL Components an inline EVD can be specified as an option. In such case comments are not allowed and the format is simply the same as for EVD in a file, just instead of newlines, commas are used to separate each field definition.

The same structure, as in above EVD Example, but as a component option (a comma separated list of fields with data types and options):

--data-definition='id int sep=";",
    name string sep=";" null="",
    birth_date date sep=";" null="1970-01-01",
    amount decimal(12,3) sep=";" thousands_sep=",",
    created_at datetime sep="\n" null="0000-00-00 00:00:00"'