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| | | What is a "Data Object "? | What is a "Data Object "? 2004-01-03 - By ashraf galal
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<html><div style='background-color:'><P class=MsoNormal style="MARGIN: 0in 0in
0pt"><TT><SPAN style="FONT-SIZE: 10pt; COLOR: black; FONT-FAMILY: 'Courier New'
">Chad;<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office"
/><o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">Regarding your first comment:<o:p><
/o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">If you have a look at the sequence
diagram attached with this class diagram (which I wasn�t able to send it to you
since the message must not be greater than 50K and it also from the book), you
will find that the business object might be stored in persistence storage.<o:p>
</o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">This persistence storage could be
any thing you like, entity bean, java class, flat file, �etc.<o:p></o:p></SPAN>
</TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">To have the big picture please get a
look to the DAO class diagram and sequence diagram this will explain more about
the data object.<o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">The term data object, we use that
term to indicate any object that persist in storage. <o:p></o:p></SPAN></TT></P
>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">The business object pattern does not
mean data object. <o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">The following is from the book too:
<o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt">Business object is an
object that implements business logic and/or business data.<o:p></o:p></SPAN><
/P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt">`<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt">Business data and
business logic are implemented in coarse-grained objects called business
objects.<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN
></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt">In J2EE, business
objects are implemented as session or entity beans.<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 10pt;
FONT-FAMILY: 'Courier New'; mso-bidi-font-size: 12.0pt">In some cases, a
business object could be an arbitrary java object that provides some services.
<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'"> <o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'"> <o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">Regarding the second comment I think
you are right. I confused you but what I want to say that we use business
delegate pattern to avoid direct invocation from the client.<o:p></o:p></SPAN><
/TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">So instantiating the pattern in
client is not recommended.<o:p></o:p></SPAN></TT></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><TT><SPAN style="FONT-SIZE: 10pt
; COLOR: black; FONT-FAMILY: 'Courier New'">But I didn�t mean to use business
delegate with the business object. since the business object (as you see from
the data access object (DAO)) is the data client. It is the object that
requires access to the data source to obtain and store data. (some of my words
from the book too). <o:p></o:p></SPAN></TT></P>
<P><BR><BR></P><BR><BR><BR>
<DIV>Ashraf Galal <BR>(416)804-8359</DIV>>From: Chad Woolley <LISTS
@(protected)>>Reply-To: An interest list for Sun Java Center J2EE
Pattern Catalog <J2EEPATTERNS-INTEREST@(protected)>>To: J2EEPATTERNS
-INTEREST@(protected) >Subject: Re: What is a "Data Object"? >Date: Fri,
2 Jan 2004 04:15:19 -0700 > >Ashraf, > >First, please ignore my
previous message where I said you only >posted the UML >diagram. Your
text came across as an attachment and I couldn't read >it in my >digest
(which is in some unreadable mime format) or on sun's site. >Plus, there >
;may be duplicates, because when I tried to post from the web form, >the page
hung >but the post still went through. That must have been what happened >
;to you too. > This isn't a very impressive site for sun, they should just do
it >like Apache's. > >Anyway, thanks for your response. I've got some
comments and >questions, which I >included inline below. &
gt; >ashraf galal wrote: > >>Chad; >> >>It is the
implementation of the business object pattern. >> >>Term: Business
Object: >> >>An object that implements business logic and/or
business data. >> >>Business data and business logic are
implemented in coarse-grained >>objects called business objects. >>
>>In J2EE, business objects are implemented as session or entity >>
;beans. >> >>In some cases, a business object could be an arbitrary
java object >>that provides some services. >>See attached document
for class and sequence diagrams >> >>I do think that these diagrams
must answer most of your questions. >> >>We might implement the
business object using the composite entity >>pattern (you are right) or
DAO or other different implementation. > >This code example is in the
"Business Object" chapter, and the UML >diagram you >attached
is from the chapter. I would think they would call it >"Business >
;Object" in the code sample if it is an occurence of that pattern. >In other
>places in the book, if a pattern uses itself "recursively", it uses >the
same name. > >Maybe that is the case, though. Maybe it is just a "simple"
>business object >that doesn't have much logic in it. It still doesn't
make sense to >call it >something different, though. > > >>
;Regarding your question �Can the Presentation Tier directly >>instantiate
and use "Data Objects"? ? >> >>We always use the business delegate
pattern to decouple the tier >>and hide the implementation details. It is
better not to use it >>directly from client tier (my opinion). > >
;Now you lost me. How is this related to the Business Delegate >pattern? if
it >was used on the client, it would probably be passed through a >
;Business Delegate, >but that doesn't tell me anythin
g more about what a "Data Object" is >or how it >is used. > >
;Thanks for your response! > >Chad > >==============================
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