“Aucun fournisseur de Persistance pour l'EntityManager” erreur

Je suis novice pour JPA, et j'ai essayé de faire un simple exemple dans le livre.
Mais peu importe ce que je fais, je reçois l'erreur suivante:

Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named EmployeeService
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:89)
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:60)
        at com.mycompany.simpleentity.EmployeeTest.main(EmployeeTest.java:18)

J'ai googlé beaucoup et j'ai fait tout ce que j'ai lu sur la JPA.

Voici un répertoire de l'arborescence de mon projet:

    .
|-- pom.xml
`-- src
    |-- main
    |   |-- java
    |   |   `-- com
    |   |       `-- mycompany
    |   |           `-- simpleentity
    |   |               |-- Employee.java
    |   |               |-- EmployeeService.java
    |   |               `-- EmployeeTest.java
    |   `-- resources
    |       `-- META-INF
    |           `-- persistence.xml
    `-- test

Voici mon pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany</groupId>
  <artifactId>SimpleEntity</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>SimpleEntity</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>javax.persistence</groupId>
      <artifactId>persistence-api</artifactId>
      <version>1.0</version>      
    </dependency>
    <dependency>
        <groupId>postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <version>9.0-801.jdbc4</version>
    </dependency>
  </dependencies>

  <build>

      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <configuration>
             <source>1.5</source>
             <target>1.5</target>
          </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>

            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath>
                        <mainClass>com.mycompany.simpleentity.EmployeeTest</mainClass>
                        <!-- <classpathLayoutType>repository</classpathLayoutType> -->
                        <classpathMavenRepositoryLayout>true</classpathMavenRepositoryLayout>
                        <classpathPrefix>${env.HOME}/.m2/repository</classpathPrefix>

                    </manifest>
                </archive>
            </configuration>
        </plugin>
      </plugins>

  </build> 
</project>

Voici mon code source:
EmployeeTest.java:

package com.mycompany.simpleentity;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class EmployeeTest {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("EmployeeService");
        EntityManager em = emf.createEntityManager();

    }
}

Et voici mon persistance.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
        http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
        version="1.0">

    <persistence-unit name="EmployeeService" transaction-type="RESOURCE_LOCAL">
        <class>com.mycompany.simpleentity.Employee</class>
        <properties>
            <property name="toplink.jdbc.driver"
                      value="org.postgresql.Driver"/>
            <property name="toplink.jdbc.url"
                      value="jdbc:postgresql://localhost:5432/testdb;create=true"/>
            <property name="toplink.jdbc.user" value="postgres"/>
            <property name="toplink.jdbc.password" value="111"/>

        </properties>
    </persistence-unit>
</persistence>

Que dois-je faire de mal?
Je vous remercie à l'avance.