Editing WinFS (section)

====Type system====
[[Image:WinFS1.svg|thumb|WinFS Type Hierarchy]]

The most important difference between a file system and WinFS is that WinFS knows the type of each data item that it stores. And the type specifies the properties of the data item. The WinFS type system is closely associated with the .NET framework's concept of [[Object-oriented programming|classes and inheritance]]. A new type can be created by [[Object-oriented programming|extending]] and nesting any predefined types.<ref name="Dev1a" />

WinFS provides four predefined base types &ndash; ''Items'', ''Relationships'', ''ScalarTypes'' and ''NestedTypes''.<ref name="Dev1a" /> An Item is the fundamental data object which can be stored, and a Relationship is the relation or link between two data items. Since all WinFS items must have a type, the type of item stored defines its properties. The properties of an Item may be a ScalarType, which defines the smallest unit of information a property can have, or a NestedType, which is a collection of more than one ScalarTypes and/or NestedTypes. All WinFS types are made available as .NET CLR [[Class (computer science)|classes]].<ref name="MSDNMag" />

Any object represented as a data unit, such as contact, image, video, document etc., can be stored in a WinFS store as a specialization of the Item type.<ref name="MSDNMag" /> By default, WinFS provides Item types for Files, Contact, Documents, Pictures, Audio, Video, Calendar, and Messages. The File Item can store any generic data, which is stored in file systems as files. But unless an advanced schema is provided for the file, by defining it to be a specialized Item, WinFS will not be able to access its data. Such a file Item can only support being related to other Items.<ref name="Dev1a" />

[[Image:WinFS2.svg|thumb|Defining a new Type]]

A developer can extend any of these types, or the base type Item, to provide a type for their custom data. The data contained in an Item is defined in terms of properties, or fields that hold the actual data. For example, an Item ''Contact'' may have a field ''Name'' that is a ScalarType, and one field ''Address'', a NestedType, which is further composed of two ScalarTypes. To define this type, the base class Item is extended and the necessary fields are added to the class.<ref name="Dev1a" /> A NestedType field can be defined as another class that contains the two ScalarType fields. Once the type is defined, a schema has to be defined, which denotes the primitive type of each field, for example, the Name field is a String, the Address field is a custom defined Address class, both the fields of which are Strings. Other primitive types that WinFS supports are [[Integer]], [[Byte]], [[Decimal#Decimal fractions|Decimal]], [[IEEE 754|Float]], [[Double precision|Double]], [[Boolean data type|Boolean]] and DateTime, among others.<ref name="Dev1a" /> The schema will also define which fields are mandatory and which are optional.<ref name="Dev2">{{cite web | url = http://msdn2.microsoft.com/en-us/library/ms996631.aspx | title = A Developer's Perspective on WinFS: Part 2 |date=July 2004 | access-date = 2007-06-30 | author = Shawn Wildermuth | work = MSDN | publisher = Microsoft }}</ref> The Contact Item defined in this way will be used to store information regarding the Contact, by populating the properties field and storing it. Only those fields marked as mandatory needs to be filled up during initial save.<ref name="MSDNMag" /> Other fields may be populated later by the user, or not populated at all. If more properties fields, such as ''last conversed date'', need to be added, this type can be extended to accommodate them. Item types for other data can be defined similarly.

[[Image:WinFS3.svg|thumb|Relationships]]

WinFS creates [[RDBMS|tables]] for all defined Items.<ref name="Dev2" /> All the fields defined for the Item form the columns of the table and all instances of the Item are stored as rows in the table for the respective Items. Whenever some field in the table refers to data in some other table, it is considered a relationship. The schema of the relationship specifies which tables are involved and what the kind and name of the relationship is. The WinFS runtime manages the relationship schemas.<ref name="MSDNMag" /> All Items are exposed as .NET CLR [[Object-oriented programming|objects]], with a uniform interface providing access to the data stored in the fields. Thus any application can retrieve object of any Item type and can use the data in the object, without being aware of the physical structure the data was stored in.<ref name="Dev1a" />

WinFS types are exposed as .NET classes, which can be instantiated as .NET objects. Data are stored in these type instances by setting their properties. Once done, they are persisted into the WinFS store. A WinFS store is accessed using an ''ItemContext'' class (see [[#Data retrieval|Data retrieval]] section for details). ItemContext allows transactional access to the WinFS store; i.e. all the operations since binding an ItemContext object to a store till it is closed either all succeed or are all rolled back. As changes are made to the data, they are not written to the disc; rather they are written to an in-memory log. Only when the connection is closed are the changes written to the disc in a batch. This helps to optimize disc I/O.<ref name="DotNetShow" /> The following code snippet, written in [[C Sharp (programming language)|C#]], creates a contact and stores it in a WinFS store.

<syntaxhighlight lang="csharp">
// Connect to the default WinFS store
using (ItemContext ic = ItemContext.Open())
{
    // Create the contact and set the data in appropriate properties
    ContactEAddress contact = new ContactEAddress {
        Name = new PersonName {                      // Name is a ComplexType
            Displayname = "Doe, John",
            FirstName = "John",
            LastName = "Doe"
        },
        TelephoneNumber = new TelephoneNumber {     // Telephone number is a ComplexType
            Country = CountryCode.Antarctica,
            Areacode = 4567,
            Number = 9876543210
        },
        Age = 111                                     // Age is a SimpleType
   };

   // Add the object to the user's personal folder.
   // This relates the item with the folder pseudo-type, for backward
   // compatibility, as this lets the item to be accessed in a folder 
   // hierarchy for apps which are not WinFS native.
   Folder containingFolder = UserDataFolder.FindMyPersonalFolder();
   containingFolder.OutFolderMemberRelationship.AddItem(ic, contact);

   // Find a document and relate with the document. Searching begins by creating an
   // ItemSearcher object. Each WinFS type object contains a GetSearcher() method
   // that generates an ItemSearcher object which searches documents of that type.
   using (ItemSearcher searcher = Document.GetSearcher(ic))
   {
        Document d = searcher.Find(@"Title = 'Some Particular Document'");
        d.OutAuthoringRelationship.AddItem(ic, contact);
   }
   // Since only one document is to be found, the ItemContext.FindOne() method
   // could be used as well.

   // Find a picture and relate with it
   using (ItemSearcher searcher = Picture.GetSearcher(ic))
   {
        Picture p = searcher.Find(@"Occasion = 'Graduation' and Sequence = '3'");
        p.OutSubjectRelationship.AddItem(ic, contact);
   }

   // Persist to the store and close the reference to the store
   ic.Update();
}
</syntaxhighlight>