Converting XML to JSON using XML Schema

Question

I would like to convert XML into JSON (concretely, a OAI-PMH response). I am currently using node.js xml2js, but the issue is that JSON is very verbose, with way to many levels of nesting and arrays, even when there is only one element as a child and will never be more than one. The issue is that xml2js does not know anything about the schema of the XML file, so it has to be conservative.

My question is, is there any other (preferably JavaScript) code which would use XML Schema to guide conversion process? So if schema defines types and structure of XML, that than JSON takes advantage of this and have correct types automatically, and not unnecessary array levels.

Answer 1

I had a similar, but opposite, problem with X2JS : it would not create a list if there was only one child element ( even when it should be a list ). The solution ( for me ) was to supply the extra options "arrayFormPaths" to the converter -- this causes matching elements to become an array, even if there is only one element.

I agree that there should be a way to do this using an XML Schema...but I couldn't find anything either.

Answer 2

At the end, I decided just to implement such a package: xml4js.

So for XML taken from XML Primer:

<?xml version="1.0"?>
<purchaseOrder orderDate="1999-10-20" xmlns="http://www.example.com/PO">
   <shipTo country="US">
      <name>Alice Smith</name>
      <street>123 Maple Street</street>
      <city>Mill Valley</city>
      <state>CA</state>
      <zip>90952</zip>
   </shipTo>
   <billTo country="US">
      <name>Robert Smith</name>
      <street>8 Oak Avenue</street>
      <city>Old Town</city>
      <state>PA</state>
      <zip>95819</zip>
   </billTo>
   <comment>Hurry, my lawn is going wild!</comment>
   <items>
      <item partNum="872-AA">
         <productName>Lawnmower</productName>
         <quantity>1</quantity>
         <USPrice>148.95</USPrice>
         <comment>Confirm this is electric</comment>
      </item>
      <item partNum="926-AA">
         <productName>Baby Monitor</productName>
         <quantity>1</quantity>
         <USPrice>39.98</USPrice>
         <shipDate>1999-05-21</shipDate>
      </item>
   </items>
</purchaseOrder>

Without using a XML Schema to guide a conversion process, with explicit arrays turned on, you would get:

{
  "purchaseOrder": {
    "$": {
      "orderDate": "1999-10-20",
      "xmlns": "http://www.example.com/PO"
    },
    "shipTo": [
      {
        "$": {
          "country": "US"
        },
        "name": [
          "Alice Smith"
        ],
        "street": [
          "123 Maple Street"
        ],
        "city": [
          "Mill Valley"
        ],
        "state": [
          "CA"
        ],
        "zip": [
          "90952"
        ]
      }
    ],
    "billTo": [
      {
        "$": {
          "country": "US"
        },
        "name": [
          "Robert Smith"
        ],
        "street": [
          "8 Oak Avenue"
        ],
        "city": [
          "Old Town"
        ],
        "state": [
          "PA"
        ],
        "zip": [
          "95819"
        ]
      }
    ],
    "comment": [
      "Hurry, my lawn is going wild!"
    ],
    "items": [
      {
        "item": [
          {
            "$": {
              "partNum": "872-AA"
            },
            "productName": [
              "Lawnmower"
            ],
            "quantity": [
              "1"
            ],
            "USPrice": [
              "148.95"
            ],
            "comment": [
              "Confirm this is electric"
            ]
          },
          {
            "$": {
              "partNum": "926-AA"
            },
            "productName": [
              "Baby Monitor"
            ],
            "quantity": [
              "1"
            ],
            "USPrice": [
              "39.98"
            ],
            "shipDate": [
              "1999-05-21"
            ]
          }
        ]
      }
    ]
  }
}

But the package gives you this:

{
  "purchaseOrder": {
    "$": {
      "orderDate": "1999-10-20T00:00:00.000Z"
    },
    "shipTo": {
      "$": {
        "country": "US"
      },
      "name": "Alice Smith",
      "street": "123 Maple Street",
      "city": "Mill Valley",
      "state": "CA",
      "zip": 90952
    },
    "billTo": {
      "$": {
        "country": "US"
      },
      "name": "Robert Smith",
      "street": "8 Oak Avenue",
      "city": "Old Town",
      "state": "PA",
      "zip": 95819
    },
    "comment": "Hurry, my lawn is going wild!",
    "items": {
      "item": [
        {
          "$": {
            "partNum": "872-AA"
          },
          "productName": "Lawnmower",
          "quantity": 1,
          "USPrice": 148.95,
          "comment": "Confirm this is electric"
        },
        {
          "$": {
            "partNum": "926-AA"
          },
          "productName": "Baby Monitor",
          "quantity": 1,
          "USPrice": 39.98,
          "shipDate": "1999-05-21T00:00:00.000Z"
        }
      ]
    }
  }
}

Answer 3

Found the following project library on GitHub that does the job : Schema Aware XML to JSON translator .

This library does the job in java. It is still not fully mature but does the conversion using the Schema provided.

Answer 4

There is a very well maintained python package named xmlschema that would do that without any hassle.

Using to_dict method.

import xmlschema
import simplejson as json

my_schema = xmlschema.XMLSchema("../shiporder.xsd")
obj = my_schema.to_dict('../shiporder.xml')
# in case you want to save the json in a file
json.dumps(obj) 

You can get the example xml and xsd for ship order from w3schools. Once downloaded try to leave only one item in the ship order xml and see how the schema retains the array type. The number types are also preserved after conversion to json.

Answer 5

If you are looking for a java solution.

• A solution using standard jdk tool xjc can be found here:

  Convert xml to json with Java . With xjc one can create Java classes from an XML Schema and use JAXB tools to read in an write out data in different formats.

• If you want to convert directly from XML file, you can use this library from Json.org like described here:

  Quickest way to convert XML to JSON in Java

Answer 6

An XML schema is used for XML validation. It is not possible to convert anything with a XML schema. A schema defines the structure of an XML document. If you want to convert something you need a XSLT which is a XML transformation specification. See here how to do it in JavaScript: http://www.w3schools.com/xsl/xsl_client.asp