Deserialize to object

Here are both the code for serialization and the classes I serializes.

       private async Task writeJsonAsync()
        {
            // Notice that the write is ALMOST identical ... except for the serializer.

            //var myCars = buildObjectGraph();
            var groups = await WordsDataSource.GetGroupsAsync();
            this.DefaultViewModel["WordsGroups"] = groups;


            var serializer = new DataContractJsonSerializer(typeof(IEnumerable<WordsGroup>));
            using (var stream = await ApplicationData.Current.LocalFolder.OpenStreamForWriteAsync(
                          JSONFILENAME,
                          CreationCollisionOption.ReplaceExisting))
            {
                serializer.WriteObject(stream, groups);
            }

            resultTextBlock.Text = "Write succeeded";
        }

   [DataContract]
    public class WordsItem
    {
        public WordsItem(String no, String en, String sp)
        {
            this.No = no;
            this.En = en;
            this.Sp = sp;
        }

        [DataMember]
        public string No { get; private set; }
        [DataMember]
        public string En { get; private set; }
        [DataMember]
        public string Sp { get; private set; }
    }


    [DataContract]
    public class WordsGroup
    {
        public WordsGroup(int id, String lesson, String info)
        {
            this.Id = id;
            this.Lesson = lesson;
            this.Info = info;
            this.Items = new ObservableCollection<WordsItem>();
        }

        [DataMember]
        public int Id { get; private set; }
        [DataMember]
        public string Lesson { get; private set; }
        [DataMember]
        public string Info { get; private set; }
        [DataMember]
        public ObservableCollection<WordsItem> Items { get; set; }


        public override string ToString()
        {
            return this.Lesson;
        }
    }

Thanks, Sigurd F