XML JAXB Serializable

I use JAXB to marshall/unmarshall XML-Documents and have a few questions:

- Do I need the Serializable-Interface in all classes which JAXB uses?:

@XmlRootElement @XmlAccessorType(XmlAccessType.NONE) @XmlType(name = "Node") public class Node implements Serializable{ private static final long serialVersionUID = 12105787978166974402L; @XmlRootElement @XmlAccessorType(XmlAccessType.NONE) @XmlType(name = "User") private Set<User> subjects = new HashSet<User>(); // inner class: Serializable, too ?? @XmlRootElement @XmlAccessorType(XmlAccessType.NONE) @XmlType(name = "User") public static class User implements Serializable{{ ... } }



And another question:

Imagine I have 1000 of Users accessing and changing the XML-Document.
How does it works? Does it works automatically when using JAXB?
I mean, I only have ONE (big) XML-File and this XML-File is accessable to the WEB-Users who can change or read it.
What about dirty reads/writes and so on?

What do I have to know when doing such scenarios?

Thanks in advance for help.