Microsoft’s upcoming “Oslo” modeling initiative is about tools and languages. MGraph is the piece within the language “M” that defines values, while MSchema is for schemas, functions and constraints and MGrammar is for textual DSLs. “Oslo” is still CTP and it will take some time until all concepts are available for production use.
By then, Microsoft plans to publish an open specification, such that everyone who wants to can implement the “M” language. Their ambition is to make it be as broad as XML is today.
Anyone can implement it. We want this approach wide spread on a variety of different platforms. We want it to be as broad as Xml is today.
Douglas Purdy, A Lap around “Oslo”
Today we have lots of XML on the wire. There’s also lots of JSON.
I want to see MGraph get there as well.
Jeff Pinkston alias Pinky:-), MGraph as a data rep
What is MGraph?
MGraph at it’s base is not a language. It is a simple contract for storing structured data in form of a labeled directed graph. This is a set of nodes where each node has an optional label and a set of successors, each of which may be a node or any other object.
The idea behind that is, that every structure can be exposed as a MGraph just by implementing the following interface, which is the core API behind MGraph.
I added some comments for easier understanding.
// Exposes whatever structure as an MGraph
public interface IGraphBuilder
{
// Checks, if the object submitted is a value or a (custom) node.
bool IsNode(object value);
// Retrieves a comparer for the (custom) node objects.
IEqualityComparer NodeComparer { get; }
// Extracts the label from a (custom) node.
object GetLabel(object node);
// Extracts the successors from a (custom) node.
IEnumerable GetSuccessors(object node);
// Gets a (custom) node with a label.
object DefineNode(object label);
// Sets successors to a (custom) node.
void DefineSuccessors(object protoNode, IEnumerable successors);
}
As you see, even the node is not specified by an interface or a base class. Both labels and successors are extracted by the visiting graph builder.
If you want, read more about the MGraph Api here.
MGraph as a language
What I do care more about is how MGraph’s textual notation looks like and how it compares to XML.
On MSDN you can find a language specification covering MSchema and MGrammar which both use parts of MGraph, but in a slightly different manner. Microsoft definitely plans to bring those pieces together.
Today MGraph is used for values in MSchema extent initializers as well as for the AST (Abstract Syntax Tree) productions in MGrammar.
The basic syntax of MGraph very similar to JSON:
label {
otherLabel { "value" },
"value",
},
"value"
As mentioned previously a successor can be either a node or a value. A value is just written directly, while a node is split into a label followed by its comma-separated successors within curly braces.
The same data as a XML-fragment would look like this:
One of the major differences is, that MGraph doesn’t distinguish attributes and elements. As XML is used today, anyone use attributes and elements according to their personal taste anyway.
Typed values
The next great difference is, that values are not just strings, but typed. Some of the intrinsic types are Text, Logical or Number.
mynode
{
text { "some text" },
number { 1234 }
logical { true }
}
Find a list of the supported types in chapter 3.5 Intrinsic Types in the “Oslo” Modeling Language Specification.
Escaped Labels
While XML-elements and attributes are restricted to QName, a label in MGraph can be any object. They way how this is expressed in the textual syntax is not finished yet, but in MGrammar productions more complex strings are defined with an id-function.
id("some label xyz")
{
true,
id("another node") { "value" }
}
Ordered and unordered successors
In order to make a mapping to relational structures easier, successors are not sorted by default. In order to sort the successors, they have to be encapsulated in an integer-labeled node.
{
0 { "value1" },
1 { "value2" }
}
Which alternatively also can be expressed by brackets instead of braces. In the “M” jargon this is called a sequence.
Single successor nodes, or labeled values
A named value in MGraph is just a labeled node with a single value successor. The equals-sign is just some syntactic sugar for better read- and writability. In the “M” jargon this is called Entity, but this name is subject to change. Record structure might be a better name.
person
{
name = "John Smith",
age = 24
}
equals to
person
{
name { "John Smith" },
age { 24 }
}
Better than XML?
XML is great. Mostly because it can be read by almost every system, not because it has such a nice syntax. It was never meant for the purpose it is used for today either. It is a markup language for defining additional metadata onto text.
But what XML is broadly used for today, is configuration files, transport messages and even internal DSLs. For this kind of information, that has more structuring elements than data, XML is way to verbose.
Therefore I think MGraph with its tight syntax has the potential to become a great and broad alternative.
What do you think?
Comparing XML, JSON and MGraph
Continue reading →
And yes, I’ll be blogging about my web-layout DSL 🙂
Lars Corneliussen 