gis-metadata-parser

XML parsers for GIS metadata that are designed to read in, validate, update and output a core set of properties that have been mapped between the most common standards, currently:

• FGDC
• ISO-19139 (and ISO-19115)
• ArcGIS (tested with ArcGIS format 1.0).

This library is compatible with Python versions 2.7 and 3.4 through 3.6.

Installation

Install with pip install gis-metadata-parser.

Usage

Parsers can be instantiated from files, XML strings or URLs. They can be converted from one standard to another as well.

from gis_metadata.arcgis_metadata_parser import ArcGISParser
from gis_metadata.fgdc_metadata_parser import FgdcParser
from gis_metadata.iso_metadata_parser import IsoParser
from gis_metadata.metadata_parser import get_metadata_parser

# From file objects
with open(r'/path/to/metadata.xml') as metadata:
    fgdc_from_file = FgdcParser(metadata)

with open(r'/path/to/metadata.xml') as metadata:
    iso_from_file = IsoParser(metadata)

# Detect standard based on root element, metadata
fgdc_from_string = get_metadata_parser(
    """
    <?xml version='1.0' encoding='UTF-8'?>
    <metadata>
        <idinfo>
        </idinfo>
    </metadata>
    """
)

# Detect ArcGIS standard based on root element and its nodes
iso_from_string = get_metadata_parser(
    """
    <?xml version='1.0' encoding='UTF-8'?>
    <metadata>
        <dataIdInfo/></dataIdInfo>
        <distInfo/></distInfo>
        <dqInfo/></dqInfo>
    </metadata>
    """
)

# Detect ISO standard based on root element, MD_Metadata or MI_Metadata
iso_from_string = get_metadata_parser(
    """
    <?xml version='1.0' encoding='UTF-8'?>
    <MD_Metadata>
        <identificationInfo>
        </identificationInfo>
    </MD_Metadata>
    """
)

# Convert from one standard to another
fgdc_converted = iso_from_file.convert_to(FgdcParser)
iso_converted = fgdc_from_file.convert_to(IsoParser)
arcgis_converted = iso_converted.convert_to(ArcGISParser)

# Output supported properties as key value pairs (dict)
fgdc_key_vals = fgdc_from_file.convert_to(dict)
iso_key_vals = iso_from_file.convert_to(dict)

Finally, the properties of the parser can be updated, validated, applied and output:

with open(r'/path/to/metadata.xml') as metadata:
    fgdc_from_file = FgdcParser(metadata)

# Example simple properties
fgdc_from_file.title
fgdc_from_file.abstract
fgdc_from_file.place_keywords
fgdc_from_file.thematic_keywords

# :see: gis_metadata.utils.SUPPORTED_PROPS for list of all supported properties

# Complex properties
fgdc_from_file.attributes
fgdc_from_file.bounding_box
fgdc_from_file.contacts
fgdc_from_file.dates
fgdc_from_file.digital_forms
fgdc_from_file.larger_works
fgdc_from_file.process_steps
fgdc_from_file.raster_info

# :see: gis_metadata.utils.COMPLEX_DEFINITIONS for structure of all complex properties

# Update properties
fgdc_from_file.title = 'New Title'
fgdc_from_file.dates = {'type': 'single' 'values': '1/1/2016'}

# Apply updates
fgdc_from_file.validate()                                      # Ensure updated properties are valid
fgdc_from_file.serialize()                                     # Output updated XML as a string
fgdc_from_file.write()                                         # Output updated XML to existing file
fgdc_from_file.write(out_file_or_path='/path/to/updated.xml')  # Output updated XML to new file

Extending and Customizing

Tips

There are a few unwritten (until now) rules about the way the metadata parsers are wired to work:

1. Properties are generally defined by XPATH in each parser._data_map
2. Simple parser properties accept only values of string and list's of string's
3. XPATH's configured in the data map support references to element attributes: 'path/to/element/@attr'
4. Complex parser properties are defined by custom parser/updater functions instead of by XPATH
5. Complex parser properties accept values of type dict containing simple properties, or a list of said dict's
6. XPATH keys in the data map with leading underscores are parsed, but not validated or written out
7. XPATH keys in the data map that "shadow" other properties but with a leading underscore serve as secondary values
8. Secondary values are used in the absence of a primary value if primary location (element or attribute) is missing
9. Additional underscores indicate further locations to check for missing values, i.e. title, _title, __title

Some examples of existing secondary properties are as follows:

# In the ArcGIS parser for distribution contact phone:

ARCGIS_TAG_FORMATS = frozendict({
     ...
    'dist_phone': 'distInfo/distributor/distorCont/rpCntInfo/cntPhone/voiceNum',
    '_dist_phone': 'distInfo/distributor/distorCont/rpCntInfo/voiceNum',  # If not in cntPhone
    ...
})

# In the FGDC parser for sub-properties in the contacts definition:

FGDC_DEFINITIONS = dict({k: dict(v) for k, v in iteritems(COMPLEX_DEFINITIONS)})
FGDC_DEFINITIONS[CONTACTS].update({
    '_name': '{_name}',
    '_organization': '{_organization}'
})
...
class FgdcParser(MetadataParser):
    ...
    def _init_data_map(self):
        ...
        ct_format = FGDC_TAG_FORMATS[CONTACTS]
        fgdc_data_structures[CONTACTS] = format_xpaths(
            ...
            name=ct_format.format(ct_path='cntperp/cntper'),
            _name=ct_format.format(ct_path='cntorgp/cntper'),  # If not in cntperp
            organization=ct_format.format(ct_path='cntperp/cntorg'),
            _organization=ct_format.format(ct_path='cntorgp/cntorg'),  # If not in cntperp
        )

# Also see the ISO parser for secondary and tertiary sub-properties in the attributes definition:

ISO_DEFINITIONS = dict({k: dict(v) for k, v in iteritems(COMPLEX_DEFINITIONS)})
ISO_DEFINITIONS[ATTRIBUTES].update({
    '_definition_source': '{_definition_src}',
    '__definition_source': '{__definition_src}',
    '___definition_source': '{___definition_src}'
})

Examples

Any of the supported parsers can be extended to include more of a standard's supported data. In this example we'll add two new properties to the IsoParser:

• metadata_language: a simple string field describing the language of the metadata file itself (not the dataset)
• metadata_contacts: a complex structure with contact info leveraging and enhancing the existing contact structure

This example will cover:

1. Adding a new simple property
2. Configuring a secondary location for a property value
3. Referencing an element attribute in an XPATH
4. Adding a new complex property
5. Customizing the complex property to include a new sub-property

Also, this example is specifically covered by unit tests.

from gis_metadata.iso_metadata_parser import IsoParser
from gis_metadata.utils import COMPLEX_DEFINITIONS, CONTACTS, format_xpaths, ParserProperty


class CustomIsoParser(IsoParser):

    def _init_data_map(self):
        super(CustomIsoParser, self)._init_data_map()

        # 1. Basic property: text or list (with secondary location referencing `codeListValue` attribute)

        lang_prop = 'metadata_language'
        self._data_map[lang_prop] = 'language/CharacterString'                    # Parse from here if present
        self._data_map['_' + lang_prop] = 'language/LanguageCode/@codeListValue'  # Otherwise, try from here

        # 2. Complex structure (reuse of contacts structure plus phone)

        # 2.1 Define some basic variables
        ct_prop = 'metadata_contacts'
        ct_xpath = 'contact/CI_ResponsibleParty/{ct_path}'
        ct_defintion = COMPLEX_DEFINITIONS[CONTACTS]
        ct_defintion['phone'] = '{phone}'

        # 2.2 Reuse CONTACT structure to specify locations per prop (adapted from parent to add `phone`)
        self._data_structures[ct_prop] = format_xpaths(
            ct_defintion,
            name=ct_xpath.format(ct_path='individualName/CharacterString'),
            organization=ct_xpath.format(ct_path='organisationName/CharacterString'),
            position=ct_xpath.format(ct_path='positionName/CharacterString'),
            phone=ct_xpath.format(
                ct_path='contactInfo/CI_Contact/phone/CI_Telephone/voice/CharacterString'
            ),
            email=ct_xpath.format(
                ct_path='contactInfo/CI_Contact/address/CI_Address/electronicMailAddress/CharacterString'
            )
        )

        # 2.3 Set the contact root to insert new elements at "contact" level given the defined path:
        #   'contact/CI_ResponsibleParty/...'
        # By default we would get multiple "CI_ResponsibleParty" elements under a single "contact"
        # This way we get multiple "contact" elements, each with its own single "CI_ResponsibleParty"
        self._data_map['_{prop}_root'.format(prop=ct_prop)] = 'contact'

        # 2.4 Leverage the default methods for parsing complex properties (or write your own parser/updater)
        self._data_map[ct_prop] = ParserProperty(self._parse_complex_list, self._update_complex_list)

        # 3. And finally, let the parent validation logic know about the two new custom properties

        self._metadata_props.add(lang_prop)
        self._metadata_props.add(ct_prop)


with open(r'/path/to/metadata.xml') as metadata:
    iso_from_file = CustomIsoParser(metadata)

iso_from_file.metadata_language
iso_from_file.metadata_contacts