GP Card Spec2.1 -- Some questions

Question

Hello all,
After i read the GP Card Spec 2.1, i get something confused,
maybe these questions appear somewhere in GP21 spec and i lost it,
if so, forgive me.
below are my questions:
1. is each Executable Load File loaded on the card needs to associate itself to
a Security Domain? if didn't specify the Security Domain AID when Upload file,
is it associated to the Issuer Security Domain?
2. the APDU command "PUT KEY", and "STORE DATA"
where do the keys actually put to? i mean, if i select my Application, and issue the
"PUT KEY" command, where does the key actually store?
should i write a process method to deal with this command and store it by myself?
the same question as STORE DATA.
3. the Open Platform Environment seems like Java Card's JCRE, is it?
the spec says not recommand to associate Applications with Issuer Security Domain,
but it seems not so easy to write my own Security Domain, are there documents or
example source codes about writing Security Domains?
is associated with Issuer Security Domain may have some drawbacks?
Thanks for any advice.

Answer 1

o When load my applet onto the card, the "LOAD" command can specify SD AID, means associate with the SD in this spec, and in the future use, my applet can use this SD's service, like
the javacard code segment:
ProviderSecurityDomain sd = OPSystem.getSecurityDomain();
// if i have got the SD, can use it's service (interface), wrap(), unwrap(),... etc.
sd.unwrap();
if i didn't specify the SD AID when loading my applet, is this "OPSystem.getSecurityDomain()" returns ISD, or just an error?
o I need to handle "STORE DATA" APDU myself, is this means i need to handle "PUT KEY" myself? that is, using an object like "DESKey" to store the "Key" when getting the command "PUT KEY"?
Thanks a lot.