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+#
+msgid ""
+msgstr ""
+
+msgid ""
+"title: A Relational Model of Data for Large Shared Data Banks - article-"
+"review"
+msgstr ""
+
+msgid "date: 2021-04-29"
+msgstr ""
+
+msgid "layout: post"
+msgstr ""
+
+msgid "lang: en"
+msgstr ""
+
+msgid ""
+"ref: a-relational-model-of-data-for-large-shared-data-banks-article-review"
+msgstr ""
+
+msgid ""
+"This is a review of the article \"[A Relational Model of Data for Large "
+"Shared Data Banks](https://www.seas.upenn.edu/~zives/03f/cis550/codd.pdf)\","
+" by E. F. Codd."
+msgstr ""
+
+msgid "Data Independence"
+msgstr ""
+
+msgid ""
+"Codd brings the idea of *data independence* as a better approach to use on "
+"databases. This is contrast with the existing approaches, namely "
+"hierarquical (tree-based) and network-based."
+msgstr ""
+
+msgid ""
+"His main argument is that queries in applications shouldn't depende and be "
+"coupled with how the data is represented internally by the database system. "
+"This key idea is very powerful, and something that we strive for in many "
+"other places: decoupling the interface from the implementation."
+msgstr ""
+
+msgid ""
+"If the database system has this separation, it can kep the querying "
+"interface stable, while having the freedom to change its internal "
+"representation at will, for better performance, less storage, etc."
+msgstr ""
+
+msgid ""
+"This is true for most modern database systems. They can change from B-Trees "
+"with leafs containing pointers to data, to B-Trees with leafs containing the"
+" raw data , to hash tables. All that without changing the query interface, "
+"only its performance."
+msgstr ""
+
+msgid ""
+"Codd mentions that, from an information representation standpoint, any index"
+" is a duplication, but useful for perfomance."
+msgstr ""
+
+msgid ""
+"This data independence also impacts ordering (a *relation* doesn't rely on "
+"the insertion order)."
+msgstr ""
+
+msgid "Duplicates"
+msgstr ""
+
+msgid ""
+"His definition of relational data is a bit differente from most modern "
+"database systems, namely **no duplicate rows**."
+msgstr ""
+
+msgid ""
+"I couldn't find a reason behind this restriction, though. For practical "
+"purposes, I find it useful to have it."
+msgstr ""
+
+msgid "Relational Data"
+msgstr ""
+
+msgid ""
+"In the article, Codd doesn't try to define a language, and today's most "
+"popular one is SQL."
+msgstr ""
+
+msgid ""
+"However, there is no restriction that says that \"SQL database\" and "
+"\"relational database\" are synonyms. One could have a relational database "
+"without using SQL at all, and it would still be a relational one."
+msgstr ""
+
+msgid ""
+"The main one that I have in mind, and the reason that led me to reading this"
+" paper in the first place, is Datomic."
+msgstr ""
+
+msgid ""
+"Is uses an [edn]-based representation for datalog queries[^edn-queries], and"
+" a particular schema used to represent data."
+msgstr ""
+
+msgid ""
+"Even though it looks very weird when coming from SQL, I'd argue that it "
+"ticks all the boxes (except for \"no duplicates\") that defines a relational"
+" database, since building relations and applying operations on them is "
+"possible."
+msgstr ""
+
+msgid ""
+"Compare and contrast a contrived example of possible representations of SQL "
+"and datalog of the same data:"
+msgstr ""
+
+msgid ""
+"-- create schema\n"
+"CREATE TABLE people (\n"
+"  id UUID PRIMARY KEY,\n"
+"  name TEXT NOT NULL,\n"
+"  manager_id UUID,\n"
+"  FOREIGN KEY (manager_id) REFERENCES people (id)\n"
+");\n"
+"\n"
+"-- insert data\n"
+"INSERT INTO people (id, name, manager_id) VALUES\n"
+"  (\"d3f29960-ccf0-44e4-be66-1a1544677441\", \"Foo\", \"076356f4-1a0e-451c-b9c6-a6f56feec941\"),\n"
+"  (\"076356f4-1a0e-451c-b9c6-a6f56feec941\", \"Bar\");\n"
+"\n"
+"-- query data, make a relation\n"
+"\n"
+"SELECT employees.name AS 'employee-name',\n"
+"       managers.name AS 'manager-name'\n"
+"FROM people employees\n"
+"INNER JOIN people managers ON employees.manager_id = managers.id;\n"
+msgstr ""
+
+msgid "{% raw %}"
+msgstr ""
+
+msgid ""
+";; create schema\n"
+"#{ {:db/ident       :person/id\n"
+"   :db/valueType   :db.type/uuid\n"
+"   :db/cardinality :db.cardinality/one\n"
+"   :db/unique      :db.unique/value}\n"
+"  {:db/ident       :person/name\n"
+"   :db/valueType   :db.type/string\n"
+"   :db/cardinality :db.cardinality/one}\n"
+"  {:db/ident       :person/manager\n"
+"   :db/valueType   :db.type/ref\n"
+"   :db/cardinality :db.cardinality/one}}\n"
+"\n"
+";; insert data\n"
+"#{ {:person/id      #uuid \"d3f29960-ccf0-44e4-be66-1a1544677441\"\n"
+"   :person/name    \"Foo\"\n"
+"   :person/manager [:person/id #uuid \"076356f4-1a0e-451c-b9c6-a6f56feec941\"]}\n"
+"  {:person/id      #uuid \"076356f4-1a0e-451c-b9c6-a6f56feec941\"\n"
+"   :person/name    \"Bar\"}}\n"
+"\n"
+";; query data, make a relation\n"
+"{:find [?employee-name ?manager-name]\n"
+" :where [[?person  :person/name    ?employee-name]\n"
+"         [?person  :person/manager ?manager]\n"
+"         [?manager :person/name    ?manager-name]]}\n"
+msgstr ""
+
+msgid "{% endraw %}"
+msgstr ""
+
+msgid ""
+"(forgive any errors on the above SQL and datalog code, I didn't run them to "
+"check. Patches welcome!)"
+msgstr ""
+
+msgid ""
+"This employee example comes from the paper, and both SQL and datalog "
+"representations match the paper definition of \"relational\"."
+msgstr ""
+
+msgid ""
+"Both \"Foo\" and \"Bar\" are employees, and the data is normalized. SQL "
+"represents data as tables, and Datomic as datoms, but relations could be "
+"derived from both, which we could view as:"
+msgstr ""
+
+msgid ""
+"employee_name | manager_name\n"
+"----------------------------\n"
+"\"Foo\"         | \"Bar\"\n"
+msgstr ""
+
+msgid ""
+"[^edn-queries]: You can think of it as JSON, but with a Clojure taste. "
+"[edn]: https://github.com/edn-format/edn"
+msgstr ""
+
+msgid "Conclusion"
+msgstr ""
+
+msgid ""
+"The article also talks about operators, consistency and normalization, which"
+" are now so widespread and well-known that it feels a bit weird seeing "
+"someone advocating for it."
+msgstr ""
+
+msgid ""
+"I also stablish that `relational != SQL`, and other databases such as "
+"Datomic are also relational, following Codd's original definition."
+msgstr ""