Failed to load *.xsd file when validate XML files

[owen198]

I am trying to build a PDF file from the example (build.sh in repo: s1kd-tools-doc). An error occurred in the validation step. Therefore I individually test command as: s1kd-validate DMC-EX-A-00-00-00-00A-000A-D_000-01_EN-CA.XML, which file located at s1kd-tools/tools/s1kd-validate/examples/namespace. The error messages occurred are as follow:

# s1kd-validate DMC-EX-A-00-00-00-00A-000A-D_000-01_EN-CA.XML 
s1kd-validate: ERROR: failed to load "http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd": Attempt to load network entity

s1kd-validate: ERROR: Attempt to load network entity: http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd
s1kd-validate: ERROR: Failed to locate the main schema resource at 'http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd'.

s1kd-validate: ERROR: failed to load "http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd": Attempt to load network entity

s1kd-validate: ERROR: Attempt to load network entity: http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd
s1kd-validate: ERROR: DMC-EX-A-00-00-00-00A-000A-D_000-01_EN-CA.XML (3): Element 'dmodule', attribute '{http://www.w3.org/2001/XMLSchema-instance}noNamespaceSchemaLocation': The document at location 'http://www.s1000d.org/S1000D_4-2/xml_schema_flat/descript.xsd' could not be acquired.
s1kd-validate: ERROR: DMC-EX-A-00-00-00-00A-000A-D_000-01_EN-CA.XML (3): Element 'dmodule': No matching global declaration available for the validation root.

It looks s1kd-validate required xsd files, but I am not sure how to locate this descript.xsd in my working directory, thanks for giving any idea about it.