C# – faster: web service or XML server output

cnetweb servicesxml

The Central Bank of Russia as any other central bank provides a service to get exchange rates between ruble a number of other world currencies.

Web service: http://www.cbr.ru/DailyInfoWebServ/DailyInfo.asmx

XML output: http://www.cbr.ru/scripts/XML_daily.asp?date_req=25/11/2009

.NET can easily read both. But what is faster and more reliable? Which could you recommend to choose?

btw, European Central Bank provides only XML output and only for today: http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml

Best Answer

Since they both come from the same source they are both just as likely to be reliable. As for speed it would be impossible to tell and is likely to fluctuate due to environmental variables that cannot be known from your question alone.

As with all things - code the solution that is the clearest, easiest to read, and easiest to maintain. Then, if performance becomes and issue, profile your application to determine if this data feed is the source of your performance problem. Then, if you have verified that it is in fact the source of the performance problem then begin investigating ways to improve the performance.

All things being equal, I would speculate that these two data feeds would be retrieved and read by your application at similar speeds.

XML escape characters

There are only five:

"   &quot;
'   &apos;
<   &lt;
>   &gt;
&   &amp;

Escaping characters depends on where the special character is used.

The examples can be validated at the W3C Markup Validation Service.

Text

The safe way is to escape all five characters in text. However, the three characters ", ' and > needn't be escaped in text:

<?xml version="1.0"?>
<valid>"'></valid>

Attributes

The safe way is to escape all five characters in attributes. However, the > character needn't be escaped in attributes:

<?xml version="1.0"?>
<valid attribute=">"/>

The ' character needn't be escaped in attributes if the quotes are ":

<?xml version="1.0"?>
<valid attribute="'"/>

Likewise, the " needn't be escaped in attributes if the quotes are ':

<?xml version="1.0"?>
<valid attribute='"'/>

Comments

All five special characters must not be escaped in comments:

<?xml version="1.0"?>
<valid>
<!-- "'<>& -->
</valid>

CDATA

All five special characters must not be escaped in CDATA sections:

<?xml version="1.0"?>
<valid>
<![CDATA["'<>&]]>
</valid>

Processing instructions

All five special characters must not be escaped in XML processing instructions:

<?xml version="1.0"?>
<?process <"'&> ?>
<valid/>

XML vs. HTML

HTML has its own set of escape codes which cover a lot more characters.

C# – Why the XPath request to XML file on web doesn’t work

Try

var node = doc.SelectSingleNode("//*[local-name()='Cube' and @currency=\"USD\""]);

you can always add in the namespace if you know it

var node = doc.SelectSingleNode("//*[local-name()='Cube' and 
     namespace-uri()='http://www.ecb.int/vocabulary/2002-08-01/eurofxref' and
     @currency=\"USD\""]);

Although it's longwinded I prefer it to trying to sort out namespace prefixes. And it also avoids the problem of the default namespace (xmlns="")