doc/man1/htsn-import.1

   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 three levels:
 160 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.
 163
 164 Default: INFO
 165
 166 .IP \fB\-\-remove\fR,\ \fB\-r\fR
 167 Remove successfully processed files. If you enable this, you can see
 168 at a glance which XML files are not being processed, because they're
 169 all that should be left.
 170
 171 Default: disabled
 172
 173 .IP \fB\-\-syslog\fR,\ \fB\-s\fR
 174 Enable logging to syslog. On Windows this will attempt to communicate
 175 (over UDP) with a syslog daemon on localhost, which will most likely
 176 not work.
 177
 178 Default: disabled
 179
 180 .SH CONFIGURATION FILE
 181 .P
 182 Any of the command-line options mentioned above can be specified in a
 183 configuration file instead. We first look for \(dqhtsn-importrc\(dq in
 184 the system configuration directory. We then look for a file named
 185 \(dq.htsn-importrc\(dq in the user's home directory. The latter will
 186 override the former.
 187 .P
 188 The user's home directory is simply $HOME on Unix; on Windows it's
 189 wherever %APPDATA% points. The system configuration directory is
 190 determined by Cabal; the \(dqsysconfdir\(dq parameter during the
 191 \(dqconfigure\(dq step is used.
 192 .P
 193 The file's syntax is given by examples in the htsn-importrc.example file
 194 (included with \fBhtsn-import\fR).
 195 .P
 196 Options specified on the command-line override those in either
 197 configuration file.
 198
 199 .SH EXAMPLES
 200 .IP \[bu] 2
 201 Import newsxml.xml into a preexisting sqlite database named \(dqfoo.sqlite3\(dq:
 202
 203 .nf
 204 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 205 .I "              test/xml/newsxml.xml"
 206 Successfully imported test/xml/newsxml.xml.
 207 Imported 1 document(s) total.
 208 .fi
 209 .IP \[bu]
 210 Repeat the previous example, but delete newsxml.xml afterwards:
 211
 212 .nf
 213 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 214 .I "              --remove test/xml/newsxml.xml"
 215 Successfully imported test/xml/newsxml.xml.
 216 Imported 1 document(s) total.
 217 Removed processed file test/xml/newsxml.xml.
 218 .fi
 219 .IP \[bu]
 220 Use a Postgres database instead of the default Sqlite. This assumes
 221 that you have a database named \(dqhtsn\(dq accessible to user
 222 \(dqpostgres\(dq locally:
 223
 224 .nf
 225 .I $ htsn-import --connection-string='dbname=htsn user=postgres' \\\\
 226 .I "              --backend=Postgres test/xml/newsxml.xml"
 227 Successfully imported test/xml/newsxml.xml.
 228 Imported 1 document(s) total.
 229 .fi
 230
 231 .SH BUGS
 232
 233 .P
 234 Send bugs to michael@orlitzky.com.