Review Writing XML  Style  Common errors 1XML Technologies David Raponi

2 Week 1 Review: 1. Style 1. Style issues Be consistent: The Title The description (same for camelCasing vs under_scores)

3XML Technologies David Raponi Week 1 Review: 1. Style 2. Common errors Be sure to group related items The book Another book The book Another book

4XML Technologies David Raponi Week 1 Review: 1. Style 2. Common errors Avoid repeated names. Examine the following:  Something that holds text  Something that holds more elements Eek! We’re using “name” to define two different structural things.

5XML Technologies David Raponi Week 1 Review: 1. Style 2. Common errors No need to increment elements! Hey! What’s the name of that book2 you’re reading? (That doesn’t make sense.) Tag names should be thought of as pure nouns. In this case, just, forget the numbers.

XML Technologies Week 2: Document Type Definitions (DTD)  What is a DTD?  How to write a DTD? 6XML Technologies David Raponi

7 Week 2: DTDs > 1. What is a DTD? 1. What is a DTD? Recall: XML is a language that can make new markup languages This involves two steps: 1.Creating own tags and structure (last week) 2.Defining that structure (DTDs, this week)

8XML Technologies David Raponi Week 2: DTDs > 1. What is a DTD? Define the blocks W3C: “The purpose of a DTD is to define the legal building blocks of an XML document.” A successful check of an XML file against a DTD makes it “valid” for that DTD (not just well-formed) Note: It still doesn’t DO anything  Sorry. … so why bother?

9XML Technologies David Raponi Week 2: DTDs > 1. What is a DTD? So why bother? Tons of data being passed around Tons of keeners coming up with their own way to manipulate the data The Apocalypse + =

10XML Technologies David Raponi Week 2: DTDs > 1. What is a DTD? Standards: ensuring predictability With a DTD, you: restrict the data content and how that content is organized This is important because if several people are passing along updated versions of an XML file, and each is trying to be clever by adding/changing things, then the file is no longer “predictable”, which would make future processing of that XML file cumbersome.  The more predictable the structure of an XML file, the easier it is to work with it

11XML Technologies David Raponi Week 2: DTDs > 1. What is a DTD? HTML goes XHTML Compare: Q: What are some differences?

12XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? 2. How to write a DTD? To write a DTD, ask yourself these questions: What elements are there? How many times are those elements allowed to appear? What is inside those elements What attributes are there?

13XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring an element Empty elements (like hr and br tags) Parsed Character Data (your text) Any Data Elements with subelements

14XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring a subelement’s recurrence How many times does the subelement appear?  Once  (do nothing, default)  Once or more  elem+  Zero or more  elem*  Zero or once  elem?  Either / or  (elem1|elem2)

15XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring a subelement’s recurrence Recurrence examples: *gnatho-what?! Dude, it’s any animal that has a jaw. Doesn’t everyone know that?

16XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring an attribute Type: CDATA (attribute values are not parsed) Enumerated (this|that|another) – specific values Value: #REQUIRED (must be present, and can’t be “ “) #IMPLIED (attr may/may not be there) #FIXED “value” (attr must always have this value) “value” (sets a default, but it can be changed)

17XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring an attribute Enumeration Examples: CDATA Examples:

18XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Declaring an attribute: special note! Spaces Recall: Spaces are NOT allowed in tag names Recall: Spaces ARE allowed in attribute values BUT: not allowed in DTD enumerated values!  Ex: (this is bad) In other words: You can have well-formed XML docs with spaces in attributes, but it may not validate with a DTD. In general: Avoid spaces in attributes! Instead, use _, -, or if you need to.

19XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Putting it together (program_v1.xml) Please open up program_v1.xml and look at it as we go through these slides…

20XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Putting it together (program_v1.xml) <!DOCTYPE program [ …(other elements to follow) ]> Begin with a doctype declaration: 

21XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml <!DOCTYPE program [ ]> Now list the next element (don’t forget the root itself!) and any sub elements it may contain 

22XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml <!DOCTYPE program [ ]> Add recurrences: (how many times the subelements appear):

23XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml To move on, state the contents of the elements in the order you listed them. The contents are one of three options: Text Another element (the cycle continues) Both (a “mixed element”)

24XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml <!DOCTYPE program [ ]> Updated:

25XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml Now keep cycling through until the elements are all accounted for: <!DOCTYPE program [ ]> Updated:

26XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? DTD for program_v1.xml Then finish up with attributes: <!DOCTYPE program [ ]> Updated:

27XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? To sum up: Doctypes are (basically) written as follows: 1.Wrap everything in the <!DOCTYPE… 2.Then list the elements with recurrences 3.List what’s inside those elements Text More elements? 4.Repeat steps 2 and 3 until all elements are accounted for 5.Declare attributes

28XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Attaching a DTD to an XML file Internal Just place the whole DTD right after your declaration External Remove the initial <!DOCTYPE declaration Save your DTD as a.dtd file Add the following to your.xml file

29XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Other notes CAPITALIZATION Note that <!ELEMENT and <!ATTLIST must be in CAPS Indenting The convention is to NOT indent your DTD items

30XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Other notes CDATA Character Data (XML engine will NOT parse the info) because the value is just text (no markup) and so it simply spits it out to screen #PCDATA Parsed Character Data (XML engine will try to interpret the contents before spitting it out) to check if there’s actually another node or special characters.  What you need to know: CDATA for attributes, #PCDATA for elements with just text

31XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Other notes Mixed Data Some text More text If you do this, let me know so I can come over and yell at you. But if you MUST, then you’d declare it like so: … or …

32XML Technologies David Raponi Week 2: DTDs > 2. How to write a DTD? Other notes XML docs are made to follow DTDs, NOT the other way around: <!DOCTYPE band [ ]> Q: Why is this technically correct, but conceptually wrong?