Use of two different array created by multi child xml parser in iOS

Here is my XML file :

<MemberBooks>
    <MemberBookDTO>
        <BookId>1</BookId>
        <Name>Dönüş</Name>
        <Author>Ayşe Kulin</Author>
        <Narrator>Ayşe Kulin</Narrator>
        <Chapters>
            <ChapterDTO>
                <Id>1</Id>
                <Name>Enrico</Name>
                <DurationAsSec>170</DurationAsSec>
            </ChapterDTO>
            <ChapterDTO>
                <Id>2</Id>
                <Name>Macias</Name>
                <DurationAsSec>176</DurationAsSec>
            </ChapterDTO>
            <ChapterDTO>
                <Id>3</Id>
                <Name>Rio</Name>
                <DurationAsSec>180</DurationAsSec>
            </ChapterDTO>
        </Chapters>
    </MemberBookDTO>
    <MemberBookDTO>
        <BookId>2</BookId>
        <Name>Flora</Name>
        <Author>Kulin</Author>
        <Narrator>Ayşe</Narrator>
        <Chapters>
            <ChapterDTO>
                <Id>4</Id>
                <Name>Coco</Name>
                <DurationAsSec>270</DurationAsSec>
            </ChapterDTO>
            <ChapterDTO>
                <Id>5</Id>
                <Name>Dominic</Name>
                <DurationAsSec>126</DurationAsSec>
            </ChapterDTO>
            <ChapterDTO>
                <Id>6</Id>
                <Name>Margareiti</Name>
                <DurationAsSec>130</DurationAsSec>
            </ChapterDTO>
            <ChapterDTO>
                <Id>7</Id>
                <Name>Vito</Name>
                <DurationAsSec>150</DurationAsSec>
            </ChapterDTO>
        </Chapters>
    </MemberBookDTO>
</MemberBooks>

My code:

- (void) parser:(NSXMLParser *)parser didStartElement:(NSString *)elementname namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
if ([elementname isEqualToString:@"MemberBookDTO"])
{
    currentBook = [[BookListInfo alloc] init];
    currentNodeContentBook=[[NSMutableString alloc] init];
    isInChapterDTO = false;
}
    else if ([elementname isEqualToString:@"ChapterDTO"])
{
    //currentBook = [[BookListInfo alloc] init];
    currentNodeContentChapters=[[NSMutableString alloc] init];
    isInChapterDTO = true;
    currentChapter = [[Chapters alloc] init];
}
}

- (void) parser:(NSXMLParser *)parser didEndElement:(NSString *)elementname namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    if(isInChapterDTO==TRUE)
    {
        if ([elementname isEqualToString:@"Id"])
        {
            currentChapter.chapterId = currentNodeContentChapters;
        }
        if ([elementname isEqualToString:@"Name"])
        {
            NSString*appendString=@"B";
            currentNodeContentChapters=[appendString   stringByAppendingString:currentNodeContentChapters];
        currentChapter.chapterName = currentNodeContentChapters;
        }
        if ([elementname isEqualToString:@"DurationAsSec"])
        {
            currentChapter.chapterDurationAsSec = currentNodeContentChapters;
        }
}
    else
    {
        if ([elementname isEqualToString:@"BookId"])
    {
            [currentNodeContentBook stringByAppendingString:currentNodeContentBook];
        currentBook.bookId = currentNodeContentBook;
        }
    if ([elementname isEqualToString:@"Author"])
    {
            ......................
        }
        if ([elementname isEqualToString:@"Narrator"])
    {
            ......................
        }
    }
}
if ([elementname isEqualToString:@"MemberBookDTO"])
{
    [bookListArray addObject:currentBook];
    currentBook = nil;
    currentNodeContentBook = nil;
}
else if ([elementname isEqualToString:@"ChapterDTO"])
{
    [chapterListArray addObject:currentChapter];
    //currentBook.ChapterList.Add(currentChapter);
    currentChapter = nil;
    isInChapterDTO = false;
}

Here i am parsing this two tag: <MemberBookDTO> & <ChapterDTO> in two different array :

1. "bookListArray" which got two array with their properties.
2. "chapterListArray" got 7 array with their properties.

Now i want to count "The number of <ChapterDTO> tags in each <Chapters>". How that could be possible? And one another thing is, when i store the value into two array "bookListArray" & "chapterListArray". How can i determine which ChapterDTO is under which MemberBookDTO? If any one have any idea, please share with me. - Thanks in advance.