Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Table 3-4: Ways to Handle EntitiesActionDescriptionentities as EntityReference nodes. You must then callthe ResolveEntity method to expand a general entity.ExpandEntitiesDefault setting; expands all entities and replacesthem with their underlying text.A character entity is an XML entity that evaluates to a character and is expressedthrough the character's decimal or hexadecimal representation. For example, Aexpands to A. Character entities are mostly used to guarantee the well-formedness ofthe overall document when this is potentially broken by that character.A general entity is a normal XML entity that can expand to a string of any size, includinga single character. A general entity is always expressed through text, even when itrefers to a single character.By default, the reader makes no distinction between the types of entities and expandsthem all when needed. By setting the EntityHandling property to ExpandCharEntities,however, you can optimize entity handling by expanding the general entities only whenrequired. In this case, a call to Read expands only character entities. To expandgeneral entities, you must resort to the ResolveEntity method or to GetAttribute, if theentity is part of an attribute.The EntityHandling property can be changed on the fly; the new value takes effectwhen the next call to Read is made.A Cache for SchemasIn the validating reader class, the Schemas property represents a collection—that is, aninstance of the XmlSchemaCollection class—in which you can store one or moreschemas that you plan to use later for validation. Using the schema collection improvesoverall performance because the various schemas are held in memory and don't needto be loaded each and every time validation occurs. You can add as many XSD andXDR schemas as you want, but bear in mind that the collection must be completedbefore the first Read call is made.To add a new schema to the cache, you use the Add method of theXmlSchemaCollection object. The method has a few overloads, as follows:public void Add(XmlSchemaCollection);public XmlSchema Add(XmlSchema);public XmlSchema Add(string, string);public XmlSchema Add(string, XmlReader);The first overload populates the current collection with all the schemas defined in thegiven collection. The remaining three overloads build from different data and return aninstance of the XmlSchema class—the .NET Framework class that contains thedefinition of an XSD schema.Populating the Schema CollectionThe schema collection actually consists of instances of the XmlSchema class—a kindof compiled version of the schema. The various overloads of the Add method allow youto create an XmlSchema object from a variety of input arguments. For example,consider the following method:public XmlSchema Add(string ns,string url74