[Stanford] Introduction to databases (week 1)

终于来交作业了....

啊啊啊初学者求问！！
Department元素下的属性Code定义哪里出错了啊？
源代码是：<!ATTLIST Department  Code (CS|EE) "CS">
编译器显示错误如下：
Error messages from xmllint: /tmp/tmpGWnbEC.dtd:3: parser error : '(' required to start ATTLIST enumeration

<!ATTLIST Department Code CS|EE) 'CS'>

^

/tmp/tmpGWnbEC.dtd:3: parser error : Content error in the external subset

<!ATTLIST Department Code CS|EE) 'CS'>

^

Sorry to reply to this old theme, but I really got in trouble. Because I use the library's computer, I don't know how to change the language to Chinese. Anyway, I have a problem for exercise one.
The exercise one is:
In this question, you are to create a DTD for a small XML data set drawn from the Stanford course catalog. There are multiple departments, each with a department chair, some courses, and professors and/or lecturers who teach courses. The XML data is here.

Write a DTD for the XML data set.

Important: Do not include <!DOCTYPE Course_Catalog [...]> in your DTD. Your DTD should start with <!ELEMENT Course_Catalog (Department*)>.

What I wrote is:
<!ELEMENT Course_Catalog (Department*)>
<!ELEMENT Department (Title, Chair, Course*)>
<!ELEMENT Department Code (#PCDATA) #REQUIRED>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Chair (Professor)>
<!ELEMENT Professor (First_Name, Last_Name)>
<!ELEMENT First_Name (#PCDATA)>
<!ELEMENT Last_Name (#PCDATA)>
<!ELEMENT Course (Title, Description?, Instructors, Prerequisites?)>
<!ELEMENT Course    Number PCDATA #REQUIRED
                    Enrollment CDATA #REQUIRED>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Description (#PCDATA)>
<!ELEMENT Instructors (Lecturer | Professor)*>
<!ELEMENT Lecturer (First_Name, Middle_Initial, Last_Name)>
<!ELEMENT Middle_Initial (#PCDATA)>
<!ELEMENT Prerequisites (Prereq)>
<!ELEMENT Prereq (#PCDATA)>

The error is:
Incorrect

Error messages from xmllint: /tmp/tmpdPII0D.dtd:3: parser error : xmlParseElementDecl: 'EMPTY', 'ANY' or '(' expected

<!ELEMENT Department Code (#PCDATA) #REQUIRED>

^

/tmp/tmpdPII0D.dtd:3: parser error : Content error in the external subset

<!ELEMENT Department Code (#PCDATA) #REQUIRED>

^

Could not parse DTD /tmp/tmpdPII0D.dtd

Did anyone know the reason for this error? Thank you so much!

这周课上完

求教，怎么看视频，我只能看到文字的介绍，没有视频的链接的？

现在交作业还能加学分嘛