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 weatherxml.dtd
  64
  65 .SH DATABASE SCHEMA
  66 .P
  67 At the top level, we have one table for each of the XML document types
  68 that we import. For example, the documents corresponding to
  69 \fInewsxml.dtd\fR will have a table called \(dqnews\(dq. All top-level
  70 tables contain two important fields, \(dqxml_file_id\(dq and
  71 \(dqtime_stamp\(dq. The former is unique and prevents us from
  72 inserting the same data twice. The time stamp on the other hand lets
  73 us know when the data is old and can be removed. The database schema
  74 make it possible to delete only the outdated top-level records; all
  75 transient children should be removed by triggers.
  76 .P
  77 These top-level tables will often have children. For example, each
  78 news item has zero or more locations associated with it. The child
  79 table will be named <parent>_<children>, which in this case
  80 corresponds to \(dqnews_locations\(dq.
  81 .P
  82 To relate the two, a third table may exist with name
  83 <parent>__<child>. Note the two underscores. This prevents ambiguity
  84 when the child table itself contains underscores. The table joining
  85 \(dqnews\(dq with \(dqnews_locations\(dq is thus called
  86 \(dqnews__news_locations\(dq. This is necessary when the child table
  87 has a unique constraint; we don't want to blindly insert duplicate
  88 records keyed to the parent. Instead we'd like to use the third table
  89 to map an existing child to the new parent.
  90 .P
  91 Where it makes sense, children are kept unique to prevent pointless
  92 duplication. This slows down inserts, and speeds up reads (which are
  93 much more frequent). There is a tradeoff to be made, however. For a
  94 table with a small, fixed upper bound on the number of rows (like
  95 \(dqodds_casinos\(dq), there is great benefit to de-duplication. The
  96 total number of rows stays small, so inserts are still quick, and many
  97 duplicate rows are eliminated.
  98 .P
  99 But, with a table like \(dqodds_games\(dq, the number of games grows
 100 quickly and without bound. It is therefore more beneficial to be able
 101 to delete the old games (through an ON DELETE CASCADE, tied to
 102 \(dqodds\(dq) than it is to eliminate duplication. A table like
 103 \(dqnews_locations\(dq is somewhere in-between. It is hoped that the
 104 unique constraint in the top-level table's \(dqxml_file_id\(dq will
 105 prevent duplication in this case anyway.
 106 .P
 107 UML diagrams of the resulting database schema for each XML document
 108 type are provided with the \fBhtsn-import\fR documentation.
 109
 110 .SH XML Schema Oddities
 111 .P
 112 There are a number of problems with the XML on the wire. Even if we
 113 construct the DTDs ourselves, the results are sometimes
 114 inconsistent. Here we document a few of them.
 115
 116 .IP \[bu]
 117 2 Odds_XML.dtd
 118
 119 The <Notes> elements here are supposed to be associated with a set of
 120 <Game> elements, but since the pair
 121 (<Notes>...</Notes><Game>...</Game>) can appear zero or more times,
 122 this leads to ambiguity in parsing. We therefore ignore the notes
 123 entirely (although a hack is employed to facilitate parsing).
 124
 125 .IP \[bu]
 126 weatherxml.dtd
 127
 128 There appear to be two types of weather documents; the first has
 129 <listing> contained within <forecast> and the second has <forecast>
 130 contained within <listing>. While it would be possible to parse both,
 131 it would greatly complicate things. The first form is more common, so
 132 that's all we support for now.
 133
 134 .SH OPTIONS
 135
 136 .IP \fB\-\-backend\fR,\ \fB\-b\fR
 137 The RDBMS backend to use. Valid choices are \fISqlite\fR and
 138 \fIPostgres\fR. Capitalization is important, sorry.
 139
 140 Default: Sqlite
 141
 142 .IP \fB\-\-connection-string\fR,\ \fB\-c\fR
 143 The connection string used for connecting to the database backend
 144 given by the \fB\-\-backend\fR option. The default is appropriate for
 145 the \fISqlite\fR backend.
 146
 147 Default: \(dq:memory:\(dq
 148
 149 .IP \fB\-\-log-file\fR
 150 If you specify a file here, logs will be written to it (possibly in
 151 addition to syslog). Can be either a relative or absolute path. It
 152 will not be auto-rotated; use something like logrotate for that.
 153
 154 Default: none
 155
 156 .IP \fB\-\-log-level\fR
 157 How verbose should the logs be? We log notifications at three levels:
 158 INFO, WARN, and ERROR. Specify the \(dqmost boring\(dq level of
 159 notifications you would like to receive (in all-caps); more
 160 interesting notifications will be logged as well.
 161
 162 Default: INFO
 163
 164 .IP \fB\-\-remove\fR,\ \fB\-r\fR
 165 Remove successfully processed files. If you enable this, you can see
 166 at a glance which XML files are not being processed, because they're
 167 all that should be left.
 168
 169 Default: disabled
 170
 171 .IP \fB\-\-syslog\fR,\ \fB\-s\fR
 172 Enable logging to syslog. On Windows this will attempt to communicate
 173 (over UDP) with a syslog daemon on localhost, which will most likely
 174 not work.
 175
 176 Default: disabled
 177
 178 .SH CONFIGURATION FILE
 179 .P
 180 Any of the command-line options mentioned above can be specified in a
 181 configuration file instead. We first look for \(dqhtsn-importrc\(dq in
 182 the system configuration directory. We then look for a file named
 183 \(dq.htsn-importrc\(dq in the user's home directory. The latter will
 184 override the former.
 185 .P
 186 The user's home directory is simply $HOME on Unix; on Windows it's
 187 wherever %APPDATA% points. The system configuration directory is
 188 determined by Cabal; the \(dqsysconfdir\(dq parameter during the
 189 \(dqconfigure\(dq step is used.
 190 .P
 191 The file's syntax is given by examples in the htsn-importrc.example file
 192 (included with \fBhtsn-import\fR).
 193 .P
 194 Options specified on the command-line override those in either
 195 configuration file.
 196
 197 .SH EXAMPLES
 198 .IP \[bu] 2
 199 Import newsxml.xml into a preexisting sqlite database named \(dqfoo.sqlite3\(dq:
 200
 201 .nf
 202 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 203 .I "              test/xml/newsxml.xml"
 204 Successfully imported test/xml/newsxml.xml.
 205 Imported 1 document(s) total.
 206 .fi
 207 .IP \[bu]
 208 Repeat the previous example, but delete newsxml.xml afterwards:
 209
 210 .nf
 211 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 212 .I "              --remove test/xml/newsxml.xml"
 213 Successfully imported test/xml/newsxml.xml.
 214 Imported 1 document(s) total.
 215 Removed processed file test/xml/newsxml.xml.
 216 .fi
 217 .IP \[bu]
 218 Use a Postgres database instead of the default Sqlite. This assumes
 219 that you have a database named \(dqhtsn\(dq accessible to user
 220 \(dqpostgres\(dq locally:
 221
 222 .nf
 223 .I $ htsn-import --connection-string='dbname=htsn user=postgres' \\\\
 224 .I "              --backend=Postgres test/xml/newsxml.xml"
 225 Successfully imported test/xml/newsxml.xml.
 226 Imported 1 document(s) total.
 227 .fi
 228
 229 .SH BUGS
 230
 231 .P
 232 Send bugs to michael@orlitzky.com.