How oracle resolves names.........an analogy

Ever been asked what the hell it is you do at work and tried to relate it to everyday life?

Here is my attempt to simplify/explain in 'laymans' terms what oracle names resolution is all about

Lets pretend I'm a motorist with no sense of direction and I've a group of friends who i can call upon to tell me how to get somewhere (resolve the name i want to connect to).

I have 5 friends with me:

Tnsnames - has a 'road map' of where all the locations are
ldap - has a sat nav
ezconnect - only knows how to get somewhere if you tell him pretty much exactly where it is
hostname - only knows how to get somewhere if the country/city/street all have the same name and the people live at number 1521
nis - the wierd guy who has an old satnav that still works but no-one asks any more

Every time i 'take a journey' (do a names resolution) i could have 1 or more of these friends with me - whether these friends are there or not is determined by

names.directory_path= (list of friends)

I could have just one, or all of them in the car with me. The order i list them in is the order i ask them directions. If one of them gives me the correct directions i don't bother asking anyone else.

In most cases tnsnames seem's to be everyones best friend and he comes on 99% of all trips and rides shotgun, the others are sometimes there by default but just sit in the back and are never asked questions of. Tnsnames has been our best friend for many years since at least Oracle 7 and we can't remember further back than that....

While tnsnames is a great guy he sometimes doesn't know everything - his 'road map' might be last years version and it may be missing some new locations or have wrong pointers to locations. Generally he's pretty reliable as long as he's been kept up to date

ldap guy is the cool kid with the iphone 6+, the iwatch and knows everything about everything, if his 3g/4g connections goes though he is screwed and cant resolve anything - where tnsnames guy is still ok as his road map is in the car and doesn't rely on anything external.

ezconnect is the new kid in town, he's handy if  tnsnames is tied up (if he's staring out of the window or something - and you don't have access to him) he can tell you the way but you need to have some idea yourself where things are - he's useful though sometimes

hostname guy can't ever remember been asked where to go in the last 20 years.....

NIS guy remembers being asked something many years ago, him and hostname guy sit in silence most of the time with glum faces.....both of them are worried that when we upgrade the car there won't be a seat for them....

If none of the guys being asked knows where the location is then we throw the famous ORA-12154 (basically i don't know where you are trying to go mate).

Sometimes we get a very similar sounding reply ORA-12154 - this means we've found the address but the person we want isn't in.....

We also sometimes get ORA-12505 - this is very similar to ORA-12154 - perhaps we tried the doorbell rather than just knocking - but there is still no-one in.

Sometimes we get an ORA-12545 - this is when the street name we are looking for doesn't seem to exist - perhaps it's a misprint in the 'road map' or the satnav has a typo.

Occasionally the friends reminisce about the old friend 'oracle names' who died a few years ago - they all however blame ldap for the untimely death

Anyway - hope you enjoyed it.....