ISSN is a standard public opaque identifier for periodical publications — like magazines, government gazettes, scientific journals, and yearbooks —, assigned by the ISSN-ORG authority. ISSN is also an valid URN, with persistense assurance.

Its main function is to be a short alias for the systematic name of the publication, uniquely identifying its contents intellectual property (see ISSN-L) or its published media types.

All media types of the same periodical (same systematic name and contents authority) are gruped as one unique ID, elected between the media's ISSNs, that is the ISSN-L (short for linking ISSN) of the periodical. In this context we can say that ISSN-L is the canonical name of the periodic.

ISSN-L is a unique identifier for all versions of the serial containing the same content across different media. As defined by ISO 3297:2007, the ISSN-L provides a mechanism for collocation or linking among the different media versions of the same continuing resource.

Example from iana.org/urn-formal/issn, the same journal can have an eletronic-ISSN and a print-ISSN, which identifies its electronic and printed publications separately:

URN:ISSN:1234-1231 identifies the current print edition of "Medical News".

URN:ISSN:1560-1560 identifies the current online edition of "Medical News".

The ISSN-L linking both media versions of "Medical News" happens to be ISSN-L 1234-1231 (i.e based on the ISSN 1234-1231, designated as such in the framework of the management of the ISSN Register).

The resolution of URN:ISSN:1234-1231 should be equivalent to the resolution of URN:ISSN:1560-1560; i.e., in both cases one should find a reference to the other media version.

The example make it clear, an ISSN-L resolver MUST to convert any ISSN to its corresponding ISSN-L. In this project we adopted a lightweight SQL structure:

   CREATE TABLE issn.intcode (
      issn integer NOT NULL PRIMARY KEY,
      issn_l integer NOT NULL
    );

The core of the ISSN-L resolver solution is a SQL script wrote for PostgreSQL, in PL/pgSQL language. It also offers functions to format and validate ISSN strings from the front-end, webservices or back-end.

The project has three main issues:

1. A (SQL+PHP) "installer" that converts the (updated) "ISSN to ISSN-L" TXT table into a SQL table of integers (ISSN numbers without the check digit).
2. An SQL-service-kit for ISSN resolution.
3. A webservice formalized by an OpenAPI description, and also implemented in SQL (+PHP+NGINX), for ISSN resolution.

The set of functions was implemented in modules named by is SQL-schemas:

• The lib.sql, which offers a resolver with all "resolution operations" (RFC2169 inspired orthogonal instruction set), a converter and an ISSN handling system.

• An Nginx application (here using an PHP-middleware example) to expose the resolution into a simple and friendly set of webservice endpoints, encouraging its use as intelligible permalinks.

• Schema API, with the webservice controller, implemented as SQL function, that mediate Apache and SQL.

Run all SQL steps of src. For a default database connection, at Linux terminal, you can use:

git clone https://github.com/okfn-brasil/ISSN-L-Resolver.git
cd ISSN-L-Resolver
PGPASSWORD=postgres psql -h localhost -U postgres  issnl < src/step1-schema.sql
PGPASSWORD=postgres psql -h localhost -U postgres  issnl < src/step2-lib.sql
PGPASSWORD=postgres psql -h localhost -U postgres  issnl < src/step3-api.sql

You can test functions with no database check by psql -n, but do better using the test-kit after populating, with the step5-assert.sql, as in the instructions below.

In order to have access to the txt data of correspondence ISSN/ISSN-L, fill the form on ISSN-ORG website:

http://www.issn.org/services/online-services/access-to-issn-l-table/

then, you download a 18Mb zip file,

 issnltables.zip

but only a half (9Mb) is about "ISSN to ISSN-L" table, and, at SQL database, with numbers as integers (4 bytes), you can use less space. With issnltables2sql.php you can convert the file into SQL and then run psql to populate. See a test dump ISSN-to-ISSN-L.txt.zip

For demo you can use non-regurlar-update from ISSN-to-ISSN-L.txt.zip.

After install database (see above section) and test populating script with $ php src/step4-issnltables2sql.php, the following summarize what will express as shell-script below:

1. unzip your updated issnltables.zip in a "issnltables" folder (or the demo zip cited above)
2. run step4 with all parameter, piping to database.
3. optional, run and (visual) check tests.
4. optional, rm -r issnltables and rm issnltables.zip

# cd ISSN-L-Resolver
unzip issnltables.zip -d issnltables
php src/step4-issnltables2sql.php all | PGPASSWORD=postgres psql -h localhost -U postgres  issnl
PGPASSWORD=postgres psql -h localhost -U postgres  issnl < src/step5-assert.sql | more

The "ISSN resolver" is a simple information retrivial service that returns integer or canonical ISSNs as response. The resolution operation names was inspired in the RFC2169 jargon, for generic URNs,

• N2C = returns the canonical (preferred) URN of an input-URN.
• N2Ns = returns a set of URNs related to the input-URN.
• N2L = [not implemented] returns or redirects to the main URL of an input-URN.
• N2Ls = [not implemented] returns all the URLs related to the input-URN.
• list = retrieves all component URNs (or its metadata), when component entities exists.
• info (default) = retrieves catalographic information or metadata of the (entity of the) URN.

The letters in these standard operation names are used in the following sense:

• "C": the canonic URN string (the "official string" and unique identifier); non-RFC2169 jargon;
• "N": URN, canonical or "reference URN" (a simplified non-ambiguous version of the canonical one);
• "L": URL (main URL is a http and secondary can by also ftp and mailto URLs, see RFC2368)
• "is": "isX" stands "is a kind of X" or "is really a X";
• "2": stands "to", for convertion services.

PS: in a next version we can include also URL of the periodic, for N2U, U2C, etc.

Typical uses for resolver functions (same as step5-assert script):

  SELECT issn.isC(115);         SELECT issn.isC('8755-9994');
  -- returns          NULL          1
  SELECT issn.isN(115);         SELECT issn.isN('8755-9995');
  -- returns             1          2
  SELECT issn.n2c(8755999);     SELECT issn.n2c('8755-9994');
  -- returns           8755999      8755999
  SELECT issn.n2c(115);         SELECT issn.cast(issn.n2c(8755999));
  -- returns            67          8755-9994
  SELECT issn.n2c(8755999);     SELECT issn.cast(issn.n2c(115));
  -- returns           8755999      0000-0671
  SELECT issn.n2ns(8755999);    SELECT issn.xservice_jspack(8755999,'n2ns');
  -- returns          {8755999}     <ret status="sucess"><issn>8755-9994</issn></ret>
  SELECT issn.n2ns_formated(115);
  -- returns {0000-0671,0000-1155,0065-759X,0065-910X,0068-0540,0074-6827,1067-8166}
  SELECT issn.any_service('n2c',67,'xml');
  -- returns {"status" : 200, "result" : "<ret>115</ret>"}
  SELECT api.run_any('issn','1.0.2','67/n2c','xml', 500);
  -- returns {"status" : 500, "result" : "<ret>115</ret>"}
  SELECT api.run_byuri('issn/67/n2c.xml');
  -- returns {"status" : 200, "result" : "<ret>115</ret>"}

See /demo folder or a live demo at api.ok.org.br

For OpenApi's ISSN-API definition, see swagger.yaml (from ISSN-L-resolver/1.0.1) or http://api.ok.org.br#issn.

For server resolver middleware, see src/resolve.php. The middleware can serverd by NGINX with other API's (eg. getdoc, getfrag, etc.) as this Nginx configurartion script:

server {
        server_name api.myexample.org;
        root   /var/www/api.myexample.org;
        index  index.php index.html index.htm;
        location / {
                try_files $uri $uri/ @rewriteIt;
        }
        location  @rewriteIt {
                rewrite ^/?(issn|getfrag|trazdia|getdoc)/
                        /resolver.php?$uri  last;
                rewrite ^/?(.*)$
                        /error.php?$1       last;
        }
        location ~ \.php$ {
                try_files $uri =404;
                include /etc/nginx/fastcgi.conf;
                fastcgi_pass unix:/run/php/php7.0-fpm.sock;
        }
        # optional include snippets/ssl-myexample.org.conf;
} #end server