Object Relational features in PostgreSQL

[Robert Abi Saab]

Hi everyone. I just finished a course on PostgreSQL and I found out that
PostgreSQL doesn't provide any object relational features (as claimed in
the official documentation), except table inheritance and very limited
user defined types (I defined a UDT with 2 attributes and couldn't use
it in a table, and the trainer said it must contain 1 attribute at most
so that it can be used (as a column) in tables)



So my question is whether there is (or will be) any support for (any of)
the following:

More flexible user defined types and support for these in tables

Type inheritance

REF and DEREF data types

Nested tables

Polymorphism and more flexible casting of objects (like the TREAT
function, not only the ONLY function)

Typed tables (create table X of type Y)

Object views

User defined functions (encapsulated in the body of a user defined type)



I would be really thankful for any fast reply, because I need to report
to the management whether a migration to PostgreSQL is both efficient
and possible or not.

[Fred Moyer]

> Hi everyone. I just finished a course on PostgreSQL and I found out that

PostgreSQL doesn't provide any object relational features (as claimed in
the official documentation), except table inheritance and very limited
user defined types (I defined a UDT with 2 attributes and couldn't use
it in a table, and the trainer said it must contain 1 attribute at most
so that it can be used (as a column) in tables)
So my question is whether there is (or will be) any support for (any of)
the following:

More flexible user defined types and support for these in tables

Type inheritance

REF and DEREF data types

Nested tables Postgres has arrays - will that work? After all a table is just an array :)

Polymorphism and more flexible casting of objects (like the TREAT
function, not only the ONLY function)

Typed tables (create table X of type Y)

Object views Postgres has views.

User defined functions (encapsulated in the body of a user defined type) Postgres has api's in several different languages -
http://www.postgresql.org/docs/curre...ic/xplang.html
The best thing about it is you can write your own functions tailored to
your needs.

I would be really thankful for any fast reply, because I need to report
to the management whether a migration to PostgreSQL is both efficient
and possible or not.

It would be helpful to know what db you're comparing it against so a more
informed response can be provided. I think a lot of your anwers are out
there - you need to get both feet wet and solve a specific problem with it
to determine if it's right for your needs.

The docs http://www.postgresql.org/docs/ provide a great deal of
information which should help you. Also the mailing lists at
http://www.postgresql.org/lists.html are very helpful and answer many
questions of those new to postgres.

Regards,

Fred

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[Jeff Eckermann]

--- Robert Abi Saab <RS***@ccc.gr > wrote:

So my question is whether there is (or will be) any
support for (any of)
the following:

More flexible user defined types and support for
these in tables

Type inheritance

REF and DEREF data types

Nested tables

Polymorphism and more flexible casting of objects
(like the TREAT
function, not only the ONLY function)

Typed tables (create table X of type Y)

Object views

User defined functions (encapsulated in the body of
a user defined type)

I would be really thankful for any fast reply,
because I need to report
to the management whether a migration to PostgreSQL
is both efficient
and possible or not.

Out of curiosity, what makes these features
indispensable to your project? Are you seeking to
migrate from a DBMS that already supports those
features, and if so, what is that?

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[elein]

This will be the topic of a talk I'll be giving at OSCON in July.

The extent of Object implementation in PostgreSQL
is not as simplistic as your analysis makes it. The Object
side of object-relational includes creating datatypes which in
turn are first class objects to be used in a relational database system.
Those first class objects have structure (class), functions
(methods, operators and indexes). The relatively recent addition
of DOMAIN support enable creating subclasses of existing types,
usually base types.

PG's implementation of inheritance is not a full OO
definition of inheritance and is contrary to Codd&Date&Darwi n's
specifications for inheritance. There were other ORDBMS that did
differently or to deeper extents.

For a good understanding of some of the features you are mentioning
and as a comparison to PostgreSQL's implementation see
Paul G. Brown's book "Object-Relational Database Management: A Plumber's Guide".

I would be happy to help with additional information about the
extent of the O part or ORDBMS to help your management team.

elein
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PostgreSQL Consulting, Support & Training

PostgreSQL General Bits http://www.varlena.com/GeneralBits/
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-- Donald Knuth, The Art of Computer Programming
On Mon, Jan 26, 2004 at 10:01:19AM +0200, Robert Abi Saab wrote:

Hi everyone. I just finished a course on PostgreSQL and I found out that
PostgreSQL doesn??t provide any object relational features (as claimed in the
official documentation), except table inheritance and very limited user defined
types (I defined a UDT with 2 attributes and couldn??t use it in a table, and
the trainer said it must contain 1 attribute at most so that it can be used (as
a column) in tables)

So my question is whether there is (or will be) any support for (any of) the
following:

More flexible user defined types and support for these in tables

Type inheritance SEE Domains
REF and DEREF data types
See OIDS
Nested tables
See row types and/or arrays. Row types are not currently valid
to store in a column.
Polymorphism and more flexible casting of objects (like the TREAT function, not
only the ONLY function)

Typed tables (create table X of type Y)
See named types.
Object views
We have this but you may not recognize it as such.
User defined functions (encapsulated in the body of a user defined type)
This is an implementation detail. The functions are linked to
the type in the type definition.

I would be really thankful for any fast reply, because I need to report to the
management whether a migration to PostgreSQL is both efficient and possible or
not.

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