Web Development Limit

Hello All:

I would like to ask deep and theoretical question.

my question is:

what is the border and limit of a web developer knowledge? the web application development is a big, long and has too many branches.

where does the web developer duty starts and ends.

the IT specializations in these days are very much, for example:

Web Design
Web Development
Database Developer
Database Administrator
System Administrator
.......ETC

the technologies involved in the web development is too much also

Database (SQL Server, Oracle ...etc)
Programming (VB.NET, C# ....etc)
Operating system (Windows server , XP ....etc)
Connectivity (ODBC, OLEDB, ADO.NET ....etc)
Data Presentation (HTML, DHTML, XHTML ....etc)
Data Structure (XML, XSD ....etc)
User Interface (Java, Javascript ......etc)
new Technologies (AJAX, ....etc)

Actually I dont know what to say, but after two years of development I am feeling my self (very beginner) and really dont have a full confidence because of the lack of view and knowledge of very related technologies to .net , in addition,

when and where shall I convert a question to a Web Designer or system adminstratror?

please help because I feel like that I am drawning in the IT sea, since I am originally coming from electronics background, and working in my organization as one man show

it will be very helpfull if some one provide an illustrative graph showing the specialization in the IT and how they act as a team together and what are the duties for each post,

is there any scinece for managing the IT knowledges?

Thank you very much