Message Structure and Serialization
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The Web Service Software Factory is now maintained by the community and can be found on the Service Factory site. This content is outdated and is no longer being maintained. It is provided as a courtesy for individuals who are still using these technologies. Retired: November 2011 |
Serialization is the process of translating binary objects into a data format that can be transmitted across process boundaries, computer boundaries, and network boundaries. When serialized data reaches the destination, or endpoint, it can be deserialized back into binary objects for use by an application. Both ASMX and WCF use SOAP for messages passed between two endpoints. However, for serialization, each uses different classes that implement different rules.
ASMX uses the XmlSerializer to translate classes into XML for communication, and to translate the XML back into classes on the receiver's end. All public members are serialized unless they are marked as non-serializable using the XmlIgnoreAttribute. A large number of attributes can also be used to control the structure of the XML. For example, a property can be represented as an attribute using the XmlAttributeAttribute, or as an element using the XmlElementAttribute. The use of these attributes provides a great deal of control over how a type is serialized into XML; however, that power comes with an unfortunate downside. It may be possible to create XML structures that are not easily translated by other type systems, such as Java; XML structures that are not easily translated can hamper interoperability.
WCF uses a DataContractSerializer to perform the same translation; however, the behavior is different from the XmlSerializer. The XmlSerializer uses an implicit model where all public properties are serialized unless they are marked with the XmlIgnoreAttribute, but the DataContractSerializer uses an explicit model where the properties and/or fields that you want to serialize must be marked with a DataMemberAttribute. It is important to note that WCF can also use the XmlSerializer to perform serialization operations.
A notable difference between ASMX and WCF is the WCF ability to serialize class members regardless of the access specifier used. This means it is now possible to serialize private fields. Using this capability, you can encapsulate fields in a data type. For example, you can provide read-only access to a private field by implementing only the get method on a property. You can then serialize that private field by adding the DataMember attribute to the field in a WCF service.
Another important difference is that the DataContractSerializer generates a simplified XML structure that increases its ability to interoperate between different operating systems. In addition, the ability for users to control the XML structure is limited. This simplified structure also means that future versions of WCF will be able to target this structure for optimization. Finally, in comparison to the XmlSerializer, the serialization of data is greatly improved with the DataContractSerializer.
Recommendation
Using WCF, you can use the XmlSerializer for types that are already created. However, to maximize interoperability, it is recommended to use WCF data contracts and the DataContractSerializer. The Web Service Software Factory (ASMX) guidance package, also referred to as the ASMX guidance package, creates types that should also migrate to WCF data contracts if no additional XML serialization attributes, such as XmlAttributeAttribute, are added. The ASMX guidance package includes an XmlNamespaceAttribute to specify the namespace of the types.