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1 .TH htsn-import 1
2
3 .SH NAME
4 htsn-import \- Import XML files from The Sports Network into an RDBMS.
5
6 .SH SYNOPSIS
7
8 \fBhtsn-import\fR [OPTIONS] [FILES]
9
10 .SH DESCRIPTION
11 .P
12 The Sports Network <http://www.sportsnetwork.com/> offers an XML feed
13 containing various sports news and statistics. Our sister program
14 \fBhtsn\fR is capable of retrieving the feed and saving the individual
15 XML documents contained therein. But what to do with them?
16 .P
17 The purpose of \fBhtsn-import\fR is to take these XML documents and
18 get them into something we can use, a relational database management
19 system (RDBMS), otherwise known as a SQL database. The structure of
20 relational database, is, well, relational, and the feed XML is not. So
21 there is some work to do before the data can be imported into the
22 database.
23 .P
24 First, we must parse the XML. Each supported document type (see below)
25 has a full pickle/unpickle implementation (\(dqpickle\(dq is simply a
26 synonym for serialize here). That means that we parse the entire
27 document into a data structure, and if we pickle (serialize) that data
28 structure, we get the exact same XML document tha we started with.
29 .P
30 This is important for two reasons. First, it serves as a second level
31 of validation. The first validation is performed by the XML parser,
32 but if that succeeds and unpicking fails, we know that something is
33 fishy. Second, we don't ever want to be surprised by some new element
34 or attribute showing up in the XML. The fact that we can unpickle the
35 whole thing now means that we won't be surprised in the future.
36 .P
37 The aforementioned feature is especially important because we
38 automatically migrate the database schema every time we import a
39 document. If you attempt to import a \(dqnewsxml.dtd\(dq document, all
40 database objects relating to the news will be created if they do not
41 exist. We don't want the schema to change out from under us without
42 warning, so it's important that no XML be parsed that would result in
43 a different schema than we had previously. Since we can
44 pickle/unpickle everything already, this should be impossible.
45
46 .SH SUPPORTED DOCUMENT TYPES
47 .P
48 The XML document types obtained from the feed are uniquely identified
49 by their DTDs. We currently support documents with the following DTDs:
50 .IP \[bu] 2
51 Auto_Racing_Schedule_XML.dtd
52 .IP \[bu]
53 Heartbeat.dtd
54 .IP \[bu]
55 Injuries_Detail_XML.dtd
56 .IP \[bu]
57 injuriesxml.dtd
58 .IP \[bu]
59 newsxml.dtd
60 .IP \[bu]
61 Odds_XML.dtd
62 .IP \[bu]
63 scoresxml.dtd
64 .IP \[bu]
65 weatherxml.dtd
66
67 .SH DATABASE SCHEMA
68 .P
69 At the top level, we have one table for each of the XML document types
70 that we import. For example, the documents corresponding to
71 \fInewsxml.dtd\fR will have a table called \(dqnews\(dq. All top-level
72 tables contain two important fields, \(dqxml_file_id\(dq and
73 \(dqtime_stamp\(dq. The former is unique and prevents us from
74 inserting the same data twice. The time stamp on the other hand lets
75 us know when the data is old and can be removed. The database schema
76 make it possible to delete only the outdated top-level records; all
77 transient children should be removed by triggers.
78 .P
79 These top-level tables will often have children. For example, each
80 news item has zero or more locations associated with it. The child
81 table will be named <parent>_<children>, which in this case
82 corresponds to \(dqnews_locations\(dq.
83 .P
84 To relate the two, a third table may exist with name
85 <parent>__<child>. Note the two underscores. This prevents ambiguity
86 when the child table itself contains underscores. The table joining
87 \(dqnews\(dq with \(dqnews_locations\(dq is thus called
88 \(dqnews__news_locations\(dq. This is necessary when the child table
89 has a unique constraint; we don't want to blindly insert duplicate
90 records keyed to the parent. Instead we'd like to use the third table
91 to map an existing child to the new parent.
92 .P
93 Where it makes sense, children are kept unique to prevent pointless
94 duplication. This slows down inserts, and speeds up reads (which are
95 much more frequent). There is a tradeoff to be made, however. For a
96 table with a small, fixed upper bound on the number of rows (like
97 \(dqodds_casinos\(dq), there is great benefit to de-duplication. The
98 total number of rows stays small, so inserts are still quick, and many
99 duplicate rows are eliminated.
100 .P
101 But, with a table like \(dqodds_games\(dq, the number of games grows
102 quickly and without bound. It is therefore more beneficial to be able
103 to delete the old games (through an ON DELETE CASCADE, tied to
104 \(dqodds\(dq) than it is to eliminate duplication. A table like
105 \(dqnews_locations\(dq is somewhere in-between. It is hoped that the
106 unique constraint in the top-level table's \(dqxml_file_id\(dq will
107 prevent duplication in this case anyway.
108 .P
109 UML diagrams of the resulting database schema for each XML document
110 type are provided with the \fBhtsn-import\fR documentation.
111
112 .SH XML Schema Oddities
113 .P
114 There are a number of problems with the XML on the wire. Even if we
115 construct the DTDs ourselves, the results are sometimes
116 inconsistent. Here we document a few of them.
117
118 .IP \[bu]
119 2 Odds_XML.dtd
120
121 The <Notes> elements here are supposed to be associated with a set of
122 <Game> elements, but since the pair
123 (<Notes>...</Notes><Game>...</Game>) can appear zero or more times,
124 this leads to ambiguity in parsing. We therefore ignore the notes
125 entirely (although a hack is employed to facilitate parsing).
126
127 .IP \[bu]
128 weatherxml.dtd
129
130 There appear to be two types of weather documents; the first has
131 <listing> contained within <forecast> and the second has <forecast>
132 contained within <listing>. While it would be possible to parse both,
133 it would greatly complicate things. The first form is more common, so
134 that's all we support for now.
135
136 .SH OPTIONS
137
138 .IP \fB\-\-backend\fR,\ \fB\-b\fR
139 The RDBMS backend to use. Valid choices are \fISqlite\fR and
140 \fIPostgres\fR. Capitalization is important, sorry.
141
142 Default: Sqlite
143
144 .IP \fB\-\-connection-string\fR,\ \fB\-c\fR
145 The connection string used for connecting to the database backend
146 given by the \fB\-\-backend\fR option. The default is appropriate for
147 the \fISqlite\fR backend.
148
149 Default: \(dq:memory:\(dq
150
151 .IP \fB\-\-log-file\fR
152 If you specify a file here, logs will be written to it (possibly in
153 addition to syslog). Can be either a relative or absolute path. It
154 will not be auto-rotated; use something like logrotate for that.
155
156 Default: none
157
158 .IP \fB\-\-log-level\fR
159 How verbose should the logs be? We log notifications at four levels:
160 DEBUG, INFO, WARN, and ERROR. Specify the \(dqmost boring\(dq level of
161 notifications you would like to receive (in all-caps); more
162 interesting notifications will be logged as well. The debug output is
163 extremely verbose and will not be written to syslog even if you try.
164
165 Default: INFO
166
167 .IP \fB\-\-remove\fR,\ \fB\-r\fR
168 Remove successfully processed files. If you enable this, you can see
169 at a glance which XML files are not being processed, because they're
170 all that should be left.
171
172 Default: disabled
173
174 .IP \fB\-\-syslog\fR,\ \fB\-s\fR
175 Enable logging to syslog. On Windows this will attempt to communicate
176 (over UDP) with a syslog daemon on localhost, which will most likely
177 not work.
178
179 Default: disabled
180
181 .SH CONFIGURATION FILE
182 .P
183 Any of the command-line options mentioned above can be specified in a
184 configuration file instead. We first look for \(dqhtsn-importrc\(dq in
185 the system configuration directory. We then look for a file named
186 \(dq.htsn-importrc\(dq in the user's home directory. The latter will
187 override the former.
188 .P
189 The user's home directory is simply $HOME on Unix; on Windows it's
190 wherever %APPDATA% points. The system configuration directory is
191 determined by Cabal; the \(dqsysconfdir\(dq parameter during the
192 \(dqconfigure\(dq step is used.
193 .P
194 The file's syntax is given by examples in the htsn-importrc.example file
195 (included with \fBhtsn-import\fR).
196 .P
197 Options specified on the command-line override those in either
198 configuration file.
199
200 .SH EXAMPLES
201 .IP \[bu] 2
202 Import newsxml.xml into a preexisting sqlite database named \(dqfoo.sqlite3\(dq:
203
204 .nf
205 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
206 .I " test/xml/newsxml.xml"
207 Successfully imported test/xml/newsxml.xml.
208 Imported 1 document(s) total.
209 .fi
210 .IP \[bu]
211 Repeat the previous example, but delete newsxml.xml afterwards:
212
213 .nf
214 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
215 .I " --remove test/xml/newsxml.xml"
216 Successfully imported test/xml/newsxml.xml.
217 Imported 1 document(s) total.
218 Removed processed file test/xml/newsxml.xml.
219 .fi
220 .IP \[bu]
221 Use a Postgres database instead of the default Sqlite. This assumes
222 that you have a database named \(dqhtsn\(dq accessible to user
223 \(dqpostgres\(dq locally:
224
225 .nf
226 .I $ htsn-import --connection-string='dbname=htsn user=postgres' \\\\
227 .I " --backend=Postgres test/xml/newsxml.xml"
228 Successfully imported test/xml/newsxml.xml.
229 Imported 1 document(s) total.
230 .fi
231
232 .SH BUGS
233
234 .P
235 Send bugs to michael@orlitzky.com.