On 12/21/19 6:40 PM, Boylan, Ross wrote:
From: Adrian Klaver <adrian.kla...@aklaver.com>
Sent: Saturday, December 21, 2019 3:37 PM
This might be easier to figure out if you outline what is going on:
Since I seem to have gone on in my responses, let me do one-line answers before
the fuller ones.
1) The purpose of the migration?
Primarily to use currently supported software. Secondarily to improve data
integrity, security and auditability.
2) A general sense of what the application is and what it does.
A GUI for managing medical specimens and associated information for multiple
research studies.
3) Have you looked at the Relations tab in Access to see what if any
relationships are there?
Yes and yes. The migration program doesn't currently use that information, and
there are some complexities.
Now the more elaborate answers:
1) The purpose of the migration?
The immediate purpose of the migration is to use software that is supported.
The application currently runs on Windows 7, Office 2010 32 bit. As of Jan 14
we have to be off Win 7 because the University says so (because MS said so) and
will be disabling such systems. Office 2010, even now, can't be installed
because of licensing. We have to use Win 10, Office 2016 (even though 2019 is
available). We can do either 32 or 64 bit office and decided to target 64 bit.
We currently use Access's split database configuration, meaning the "backend"
is a file on a shared drive.
Since we had to go to the pain of migrating anyway, this seemed a good time to switch to
a server-based backend. Although the Access split configuration has worked, having
multiple users touching the same file always makes me uncomfortable, and a real database
server would seem to offer better assurances of data integrity, security, and
auditability. Since the databases store sensitive medical information, these are
concerns not only for us but for our funders and other oversight bodies. Historically,
the requirements have gotten increasingly stringent, and it seems to me there is some
possibility that the Access "backend" will fall short of the requirements in
the future.
Another consideration is that MS is increasingly deemphasizing using Access as
a data store. Of course, they want people to go to MS SQL Server. When I
visited MS's web page for Access 2016 I couldn't find any statement that it
could be used without a server-based backed, even though it can. But depending
on a feature that's getting so studiously ignored seems risky.
Finally, I had some really bad experiences--that is, lost a day--trying to get
queries to work that wouldn't, because MS Access SQL just isn't quite SQL. I
was hoping to avoid that in the future.
Because of the time pressure, we'll be sticking with the file-based backend for
now.
Alright this is the part where I got confused. I think what is going on is:
1) The immediate change is going to be to Access 2016 on Windows 10 64
keeping the data in Access files(.accdb)
2) The long term plan is to move the data from the Access files to a
stand alone SQL server, presumably Postgres. You are looking for
assistance in converting Access tables and relationships to Postgres.
3) At some point the GUI will point to the data in the server instead of
in the Access files.
Is any of the above correct?
More below.
The front-end application (described next) is built on Access and is fairly
substantial; migrating it to another platform seems not worth it.
2) A general sense of what the application is and what it does.
The application is a GUI for relatively non-computer-technical users. They run
medical research studies, and each time someone comes in various tests are
performed and recorded, and specimens collected. Other health-related
information is also collected. The core function is the management of
biological specimens that result.
We also serve as a repository for specimens collected at other sites. There
are various types of specimens and various procedures that can be performed on
each.
Researchers then query the database by outlining what kind of specimens they
want and getting a list of specimens. Usually they do it by asking me, and I
do the queries.
The actual amount of data is not trivial, but is not that large by current
standards. The file-based backends are around 20MB (after a compact and
repair), and the largest tables have around 100K records. I don't think
there's anything there that requires us to use 64 bits. The data are very
valuable, in that they represent over a decade's work, lots of $ of effort, and
without them the physical specimens would be essentially useless.
The number of users, esp simultaneous users, is also relatively small, around
10.
3) Have you looked at the Relations tab in Access to see what if any
relationships are there?
Yes, but the export program doesn't :) The relations tab documents many, but not all, of
the relations in the database. The relations are also a little tricky because sometimes
the lack of a relation should not be considered disqualifying for a specimen. Simple
example: freezer type is an id to be looked up in a small table of freezer type ids and
their names. If the freezer type is missing or nonsense, we may still want the sample.
That can be expressed as a left join; the "Access SQL is not SQL" problems
centered on left joins.
Postgres is going to be stricter about this. Access has the concept of
suggested relationships that are not enforced:
https://support.office.com/en-us/article/Guide-to-table-relationships-30446197-4fbe-457b-b992-2f6fb812b58f
"A table relationship is represented by a relationship line drawn
between tables in the Relationships window. A relationship that does not
enforce referential integrity appears as a thin line between the common
fields supporting the relationship. When you select the relationship by
clicking its line, the line thickens to indicate it is selected. If you
enforce referential integrity for this relationship, the line appears
thicker at each end. In addition, the number 1 appears over the thick
portion of the line on one side of the relationship, and the infinity
symbol (∞) appears over the thick portion of the line on the other side."
Postgres Foreign Key relationships either exist or they don't. Now you
can employee 'cheats' with you own triggers, but that is another subject.
As to your freezer example:
create table freezer_info(freezer_id int PRIMARY KEY);
create table sample_tbl(sample_id serial PRIMARY KEY, freezer_fk int
REFERENCES freezer_info ON UPDATE CASCADE);
insert into freezer_info values (1), (2);
select * from freezer_info ;
freezer_id
------------
1
2
insert into sample_tbl(freezer_fk) values (1), (null);
select * from sample_tbl;
sample_id | freezer_fk
-----------+------------
1 | 1
2 | NULL
The above will not cover the case where freezer_fk is a nonsense
value(no relation to freezer_info). In that situation you would probably
need to change the nonsense value to NULL or some placeholder value.
Ross
--
Adrian Klaver
adrian.kla...@aklaver.com
