Doesn't matter if they're "frequently asked" at this point - if you have a question, please add it to this page. We'll try to get an answer posted ASAP.
- 1 How the Heck do I Read an XML File?
- 2 Is my data file PDS4-compliant?
- 3 How do I translate FITS Header values into PDS label values?
- 4 Where Can I Find...?
- 5 Where's the Master Schema?
- 6 Where are the Discipline Dictionaries?
How the Heck do I Read an XML File?
Glad you asked! Try the How to View an XML File page on this wiki.
Is my data file PDS4-compliant?
PDS4 data structures are severely limited, and how they may be applied to data is also part of PDS4 compliance. You can find the details on what is compliant and what to look for in existing non-PDS4 data file on the PDS4 Data Structures page of this wiki.
How do I translate FITS Header values into PDS label values?
Here is a set of Notes for Labelling FITS files covering how to deal with the NAXISn values, for a start, and the other reserved FITS keywords relating to the primary data as well as IMAGE, TABLE, and BINTAB extensions.
Where Can I Find...?
- This site lists the manuals and guides produced by PDS for PDS4 users. Here you'll find the Standards Reference, the Data Dictionary, the Information Model Specification, and a collection of tutorials and handbooks on various subjects. If you're working on labels for archiving, look for the best available version under the Released subheading. Use Development versions only if you have a specific reason to.
- Here, too, look for the Released subheading.
- This includes the PDS4 Validation Tool software - the canonical validator for PDS4 data submissions, which you should probably learn to use sooner rather than later.
Standard Value Lists for PDS4 keywords
- There are three places:
- The Data Dictionary document. This is a contextual dictionary, in other words the standard value list will be dependent on what class the keyword appears in, and will be different for different classes. There's a tutorial available from the documentation page, above, on how to use the Data Dictionary. Note: This is the only source for the standard values that includes the description or definition for each of the standard values.
- In the Schematron file. If you prefer reading code to reading the Data Dictionary, or you just find it easier to search ASCII text, open the corresponding Schematron file and look for the class containing the keyword, and then the keyword itself. You should find one rule that enumerates the entire standard value list. Make sure you're looking at the correct context. If you have questions about how to read a Schematron file, ask your Friendly Neighborhood PDS Consultant.
- On the Standard Values Quick Reference page of this wiki, maintained for the convenience of SBN data preparers.
Data Type Definitions
- If you actually need to know the syntax and requirements for the data types defined in the PDS core namespace - the data types used in data structures as well as those used in creating your own mission dictionary attributes - you have two options:
- The XML Schema File and Schematron files for the pds: namespace. The .xsd file will contain the type definitions and the Schematron file will contain standard value lists for those data types that have them. You will need to be able to read enough schema to understand the definitions, of course. Your PDS node consultant can help with that.
- The data type quick-reference pages on this wiki. These pages were compiled for easy reference and contains simple verbal descriptions of the characteristics of each data type. There are two pages:
- The "PDS4 Character Data Type Definitions" page lists all the data types beginning with "ASCII_" or "UTF8_". These are the data types used in Table_Character structures an in defining local dictionary attributes.
- The "PDS4 Binary Data Type Definitions" page lists all the hardware formats permitted in PDS4 data object files.
Units of Measure Class Lists
- To facilitate unit conversion, the PDS4 schemas contain unit classes (Units_of_Length, Units_of_Temperature, etc.). Each unit class is defined as a data type with an enumerated value list containing all the recognized units belonging to that class as they must appear in your data labels. You can find these enumerated value lists in the PDS4 Data Dictionary, in the pds: core namespace Schematron file, or on the "Unit Classes Standard Values" page on this wiki.
Where's the Master Schema?
The PDS Engineering Node maintains a page for downloading the system schemas here:
It contains the PDS master schema (XSD and Schematron parts). Look for the released version at the top of the page unless you have a specific reason for using a development version, listed lower down. As discipline dictionaries are developed, they will be included on this page as well. For the moment, the master schema set is the only one listed.
Once you locate the schema version you want, you will see three files with the same file name but different extensions. As of the last update, for example, the current version is '18.104.22.168'. The files available for download are:
- This is the Master Schema File. It is an XML Schema file containing all the data structure classes, meta data classes, and data types that define the core PDS requirements. You use it to create and validate labels, Validating XML editors that understand XML Schema will be able to use this file.
- This is the companion Schematron file to the Master Schema. It contains a series of rules that enforce additional requirements, over and above what the Master Schema itself can enforce, on the attribute values and cross-relationships (like, you must use either this attribute or that one but not both). Try to find yourself a validating editor that also knows how to apply Schematron validation, and you'll save yourself some trouble later on. The PDS validation tool references both of these files.
- This is a label for the previous two schemas. If for some reason you want to reference either the Master Schema or the Schematron file in some other product label, you'll find the logical ID for them in this label. You can also use this label if you want to include the schemas as documents in a collection you're building. You don't need this file for creating or validating product labels, so you can ignore it for your own label development and validation processing.
You'll find a similarly named set of three files for all the lastest versions of the schemas on this page, serving the same functions for their respective namespaces as the above files do for the pds namespace.
Where are the Discipline Dictionaries?
Discipline dictionaries can be referenced by any label in the <Discpline_Area>, but in order to reference them in the label you need to download the schema that defines that discipline namespace and the classes and attributes within it - in other words, you need the schema form of the discipline dictionary (as opposed to a human-readable form, say).
The discipline dictionaries will be found listed on the same schema page as the Master Schema (once they are officially configured, that is):
The format for file naming follows the conventions mentioned above for the Master Schema. Make sure you also check for a corresponding Schematron file - most, if not all, discipline schemas will have a Schematron file in addition to the an XML Schema file.
In some cases, your PDS consultant may direct you to use a pre-release version of a discipline schema. In this case the corresponding file(s) will be sent directly to you by the consultant or by the discipline node.