gistfile1.js

{
	"_id" : ObjectId("4c5c5542124ba05b7c000001"),
	"leader" : "00597cz  a2200217n  4500",
	"fields" : [
		{
			"001" : "6"
		},
		{
			"005" : "19840322000000.0"
		},
		{
			"008" : "821220n| acaaaaaa           |a aaa      "
		},
		{
			"010" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "n  42000048 "
					}
				]
			}
		},
		{
			"035" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "(DLC)n  42000048"
					}
				]
			}
		},
		{
			"040" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "DLC"
					},
					{
						"c" : "DLC"
					}
				]
			}
		},
		{
			"100" : {
				"ind1" : "1",
				"ind2" : "0",
				"subfields" : [
					{
						"a" : "Asaka, Toshiki,"
					},
					{
						"d" : "1934-"
					},
					{
						"t" : "Hokuriku no kodai to chūsei"
					}
				]
			}
		},
		{
			"430" : {
				"ind1" : " ",
				"ind2" : "0",
				"subfields" : [
					{
						"a" : "Hokuriku no kodai to chūsei"
					}
				]
			}
		},
		{
			"641" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "Projected in 3 v."
					}
				]
			}
		},
		{
			"642" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "2"
					},
					{
						"5" : "DLC"
					}
				]
			}
		},
		{
			"643" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "Tokyo"
					},
					{
						"b" : "Hōsei Daigaku Shuppankyoku"
					}
				]
			}
		},
		{
			"644" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "f"
					},
					{
						"5" : "DLC"
					}
				]
			}
		},
		{
			"645" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "t"
					},
					{
						"5" : "DLC"
					}
				]
			}
		},
		{
			"646" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "s"
					},
					{
						"5" : "DLC"
					}
				]
			}
		},
		{
			"670" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "Asaka, Toshiki. Jishō Juei no nairanron josetsu. 1981."
					}
				]
			}
		},
		{
			"953" : {
				"ind1" : " ",
				"ind2" : " ",
				"subfields" : [
					{
						"a" : "xx00"
					}
				]
			}
		}
	]
}

Awesome. So the question at this point is, is this useful? I mean, it works pretty well for MongoDB, but that's because it has sort of an XPath-y like syntax to query, like "fields.245.a"

However, this is more like:
fields[5]['245'][0]['a'][0]

which is WAY awkward. So my question is, if you need a DSL to do anything with it, is it worth it at all?

Even if you went with a hash instead of an array of fields, throwing away round-tripping, you would still run into a problem with multiple fields of the same tag and multiple subfields with the same code:

fields.650[0]["a"][0]

Still gross.

But I think your original round-trippable JSON format is useful if you want to use a JSON->native mappings and use native iterators, etc, rather than having to go through the intermediary pain and additional sluggishness of a MARC or XML parsing library.

Agreed. MARC's going to suck any way you cut it.

This:
http://goessner.net/articles/JsonPath/
would make this a no-brainer, really.