XML 与逗号分隔的文本文件

Question

Ok, I've read a couple books on XML and wrote programs to spit it out and what not. But here's the question. Both a comma delimited file and a XML file are "human readable." But in general, the comma delimited file is much easier on my eyes than a XML file; the tags typically take up as much if not more space than the data. This just seems to obscure what I'm reading and the format can take a page to contain the same information that you can contain on a single line of text in a comma delimited file. And a comma delimited file is significantly less complex to parse. So the real question is why XML? Just because all the cool kids are doing it?

Answer 1

Advantages

A number of advantages XML has over CSV:

• Hierarchical data organization
• Automatic data validation (XML Schemas or DTDs)
• Easily convert formats (using XSL)
• Easy to identify relational structure
• Can be used in combination with XML-RPC
• Suitable for object persistence (marshalling)
• Simplifies business-to-business communications
• Helpful related technologies (XPath, DOM)
• Tight integration with modern Web browsers
• Extract, Transform, and Load (ETL) tools
• Backwards file format compatibility (version attribute)
• Digital signatures

It completely depends on the problem domain and what you are trying to solve.

Example

The last item is something that many people miss when writing web pages. Consider the situation where you have a large data store of songs. Songs have artists, albums, beats per minute, and so forth. You could export the data to XML, write a simple stylesheet to render the XML as XHTML, then point the browser at the XML page. The browser will render the XML as a web page.

You cannot do that with CSV.

Disadvantages

Joel Spolsky has a great article on why XML is a poor choice as a complex data store: it is slow. (Unlike a database, which can retrieve previous or next records with a single CPU instruction, traversing records in an XML document is much slower.) Arguably, this could be considered an optimization problem, resolved by waiting 18 months . Thus:

• Slower to parse than other formats
• Syntactical redundancy can detract from readability
• Document bloat could affect storage costs
• Cannot easily model overlapping (non-hierarchical) data structures
• Poorly designed XML file formats are not uncommon (in my experience; citation needed)

Related Question

See also: Why Should I Use A Human Readable File Format .

Answer 2

These aren't the only two options, you can also use JSON or YAML which are much lighter weight than xml.

In general, if you have simple tabular data with out many special characters, CSV isn't a bad choice. For structured data, consider using one of the other 3.

Answer 3

XML supports complex, structured and hierarchical representation of things. That's far from what CSV can store trivially.

Think about a complex object graph in an object oriented environment. It can be serialized as an XML document pretty easily but CSV cannot handle such a thing.

Answer 4

It all depends on what you need to do. If you need more complexity in your data structures than a simple "flat" row structure can give. for example hierarchical data, then XML is a great choice.

Answer 5

Well XML is human readable and human editable. You can look at an XML file and know exactly what it is. A CSV file is human readable but you don't really know what each value means at all.

For example, if we're storing user accounts, which would you prefer?

<user>
    <username>ryeguy</username>
    <password>abc123</password>
    <regdate>3-4-08</regdate>
    <email>my@email.com</email>
</user>

OR

ryeguy,abc123,3-4-08,my@email.com

Of course, this is just an example, but imagine it with 30 fields or so!

Or worse yet, what if we make subfields?

<user>
    <username>ryeguy</username>
    <password>abc123</password>
    <regdate>3-4-08</regdate>
    <email>my@email.com</email>
    <posts>
        <post>
            <id>34</id>
            ....
        </post>
    </posts>
</user>

That would be a pain in the ass to put in a CSV. Soon you'd be making your own querying language.

Answer 6

The fact that XML is human readable does not mean that has been made with the idea of having it read (or even edited) directly by humans.

XML has a nice set of properties that make it a good choice for many cases, in particular when you have the human resources to deal with the additional burden that such properties inevitably bring in: validation, well defined standard, a lot of tools, a very flexible architecture, it maps nicely to a tree model, which is what many programs use. Its human readability is an added value that simplifies debugging (try to do debugging of a binary file...), inspection and small changes for trivial cases.

CSV on the other hand is easy, quick and linear, although many dialects exist, and parsing it well is far from trivial (and with the added problem that it looks trivial!). For most applications involving table of data, CSV is the perfect choice.

In general, however, there are cases of data representation you can solve with XML but you cannot solve with CSV (for example, a tree). On the other hand, any data that can be represented in CSV can also be represented in XML, although it's not guaranteed (and indeed is also verified) that it will be more efficient (in terms of space, ease of parsing etc). It's a matter of "degrees of freedom" of your format. XML has a higher value of degree of freedom. CSV is lower. The hype behind XML is also relative to this fact.

Don't fall victim of the hammer syndrome: when you have a hammer (XML), everything looks like a nail (something that you have to solve with XML). Reality is much different and nuanced. XML is cool, but it's not the answer to any problem.

Answer 7

CSV was never really a standard. Just the same quick and dirty method a bunch of people came up with independently. Of course, some of these people were smarter than others and realized you needed to escape characters but others didn't. Even MSSQL exports CSVs improperly. There is a documented RIGHT way to doing XML so if you're doing it right and someone's application or whatever isn't accepting it you have some clout when you say "That's not my fault."

Answer 8

XML will describe the content and also has a ton of supporting libraries in a variety of languages... but it can be bloated. If the receiving end of the csv is aware of the layout and it is tabular, I don't see anything wrong with it.

Answer 9

Xml 可以根据合同（模式或 DTD）进行验证。

Answer 10

XML 也有围绕它的免费技术：XmlDom、XPath、XSLT、XSD、Xml Schemas

Answer 11

Among the reasons you may prefer XML over CSV (depends on the task at hand of course): * Almost all platforms and languages have existing libraries for reading, writing, parsing, and manipulating XML. * XML has well-defined rules for encoding all characters. CSV has ambiguities such as how to encode commas that are part of the data. * XML supports a variety of data shapes (like hierarchical) where as CSV is most useful when the data looks like a table (rows and columns).

Answer 12

I like to think of the primary distinction in this case as XML is TREE based, while CSV is TABLE-based.

That is, you can nest and re-nest and omit and generally make a complex TREE structure in XML, whereas you can only make simple 2D tables in CSV.