XML Database - 2

Features of the XML Database

Not all databases are the same, yet there is enough features between them that is similar to give us a rough idea of some of thebasci structure. Before we continue let us note that the database is still evolving and will continue to do so for some time.

One feature of the database is XML storage. It stores documents as a unit, and creates models that are closely related to XML or a related technology like DOM.

The model includes un-uniformed levels of complexity as well as supplementation for content and semi-structured data. Mapping is used to ensure that the XML unique model of data is managed.

After the data is stored the user will need to continue to use the NXD tools. It is not as useful as to try to access the data tables using SQL as one would think; this is because the data that would be viewed would be the model of an XML document not the entities that the data depict.

It important to note that the business entity model is within the XML document domain, not the storage system, in order to work with the actually data you will have to work with it as XML.

Another feature of the database worth mentioning is queries. Currently XPath is the query language of choice. To function as a database query language XPath is extended some what to allow queries across compilations of documents.

On a negative note XPath was not created to be a database query language so it does not function properly in that area.

In order to better the performance of queries NXDs support the development of index on the data stored in the collections.

The index can be used to improve the speed of the query execution. Fine points of what can be indexed and how the index is fashioned varies with products.

What kind of data types are supported by XML?

You might be surprised to hear that XML does not actually support any data types. The XML document is almost always text, even if by chance it does represent another datatypes ; this would be something like a date or integer.

Usually the data exchange software converts the data from a text form, like in the XML document, to other forms within the database and vice versa.

Two methods are most common in determining which conversion to do. The fist of these methods is that the software determines the type of data that is from the database schema, this works out well because it is always available at run time.

The other method that is common is that the user clearly provides the data type, like with the mapping information.

This can be recorded by the user or even generated without human intervention from a database schema or even an XML schema.

When it is generated automatically, the data types can be taken from database schemas as well as from certain types of XML schemas.The is another issue related to conversions as well, this has to do largely with what text formats are recognized when being exchanged from XML or what could be produced when exchanging data from XML.

With most situations the amount of the text formats that are supported for a specific data type is given to be some what restricted, this is seen with a single specific format or with those that are supported by a particular JDBC driver.

It is important to also note that dates will usually cause issues; this is largely due to the fact that the range of possible formats is extremely extensive. When you also consider number with international formats, these can add to the problems as well.

Concluding statements

XML may seem to be confusing, however, it is beneficial and even a bit less complicated then HTML. Yet when you are beginning to take the step to understanding XML when you have spent much time working with HTML, the process can be a bit distressing.

Never fear, once you have completed that step, XML is definitely a dominant format. It is also used in almost all of the models we have discussed, making it a vital area to explore in more detail.