Writing apps that use XML storage solutions

Virgil Bevans

I am an old Xbase programmer trying to update myself, but experiencing only minor success at this point. The problem: Converting (as a teaching exercise) a small data storage and reporting application from Visual FoxPro to C# and utilizing XML tables as the storage device. When developing the app in VFP I simply create the empty tables and then write appropriate code to append, insert or delete data. In reading some of the articles on this site and experimenting with XML tables, it appears that the table cannot exist as an empty container, but must be initialized with dummy data. That just seems wrong to me. Of course, the problem really only exist with a new install. Once the table(s) have data in them I find it easy to treat them just as I would a VFP or dBase table. Perhaps it is a matter of improper understanding or perspective. Can someone straighten me out?

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Vulpes13y ago
Yes, you're right that (apart from its basic rules) an XML document has no structure as such - you can put anything you like in there.

You could certainly give it some structure with an XML Schema Definition file (XSD) and mimic the database table schemas which you're used to.

I'd check out the W3Schools tutorial on the subject which is a good place to start:

http://www.w3schools.com/schema/
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Virgil Bevans13y ago
I was afraid my explanation wasn't clear enough. Let me offer an example. Suppose I want to create and maintain a contact list. The fields of the data table might include Name, StreetAddress, City, State, PhoneNo, etc. Now further suppose I've developed this app and just did a fresh install (no data entries yet). With VFP or even SQL my data table structure is already in existence and I could code a method that would add a record to the table which would work whether the table was empty or had a thousand entries. Something like:

USE Contacts
Append Blank
Replace FirstName With "John";
LastName With "Doe";
StreetAdd With "123 East St."

etc.

I'm led to believe that this same type of procedure (of course coded in C# and perhaps using LINQ technology) would work with an XML table as long as it had at least one entry already in it, thereby supplying a structure to the table, but a new install would have no data. Likewise, maybe the app would have a function to "reset", clearing all old records and starting over. Again no data and apparently no structure.

Is an "xsd" file the proper way to supply a structure for the table and if so, how is it used?

Again, maybe I just have a total misunderstanding of the concept.
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Vulpes13y ago
I'm not sure I know what you mean by an empty container in the context of XML but you can certainly create an XML document with just a root element and then add stuff to it as you go along:

using System;
using System.Xml.Linq;

class Test
{
static void Main()
{
var root = new XElement("root");
root.Save("virgil.xml");

// now add a new element
root.Add(new XElement("first", "some data"));
root.Save("virgil.xml");
}
}

After this program has been run, the XML file created looks like this:

some data

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