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 Heartbeat.dtd
  52 .IP \[bu]
  53 newsxml.dtd
  54 .IP \[bu]
  55 Injuries_Detail_XML.dtd
  56 .IP \[bu]
  57 injuriesxml.dtd
  58 .IP \[bu]
  59 Odds_XML.dtd
  60 .IP \[bu]
  61 weatherxml.dtd
  62
  63 .SH DATABASE SCHEMA
  64 .P
  65 At the top level, we have one table for each of the XML document types
  66 that we import. For example, the documents corresponding to
  67 \fInewsxml.dtd\fR will have a table called \(dqnews\(dq. All top-level
  68 tables contain two important fields, \(dqxml_file_id\(dq and
  69 \(dqtime_stamp\(dq. The former is unique and prevents us from
  70 inserting the same data twice. The time stamp on the other hand lets
  71 us know when the data is old and can be removed. The database schema
  72 make it possible to delete only the outdated top-level records; all
  73 transient children should be removed by triggers.
  74 .P
  75 These top-level tables will often have children. For example, each
  76 news item has zero or more locations associated with it. The child
  77 table will be named <parent>_<children>, which in this case
  78 corresponds to \(dqnews_locations\(dq.
  79 .P
  80 To relate the two, a third table may exist with name
  81 <parent>__<child>. Note the two underscores. This prevents ambiguity
  82 when the child table itself contains underscores. The table joining
  83 \(dqnews\(dq with \(dqnews_locations\(dq is thus called
  84 \(dqnews__news_locations\(dq. This is necessary when the child table
  85 has a unique constraint; we don't want to blindly insert duplicate
  86 records keyed to the parent. Instead we'd like to use the third table
  87 to map an existing child to the new parent.
  88 .P
  89 Where it makes sense, children are kept unique to prevent pointless
  90 duplication. This slows down inserts, and speeds up reads (which are
  91 much more frequent). There is a tradeoff to be made, however. For a
  92 table with a small, fixed upper bound on the number of rows (like
  93 \(dqodds_casinos\(dq), there is great benefit to de-duplication. The
  94 total number of rows stays small, so inserts are still quick, and many
  95 duplicate rows are eliminated.
  96 .P
  97 But, with a table like \(dqodds_games\(dq, the number of games grows
  98 quickly and without bound. It is therefore more beneficial to be able
  99 to delete the old games (through an ON DELETE CASCADE, tied to
 100 \(dqodds\(dq) than it is to eliminate duplication. A table like
 101 \(dqnews_locations\(dq is somewhere in-between. It is hoped that the
 102 unique constraint in the top-level table's \(dqxml_file_id\(dq will
 103 prevent duplication in this case anyway.
 104 .P
 105 UML diagrams of the resulting database schema for each XML document
 106 type are provided with the \fBhtsn-import\fR documentation.
 107
 108 .SH XML Schema Oddities
 109 .P
 110 There are a number of problems with the XML on the wire. Even if we
 111 construct the DTDs ourselves, the results are sometimes
 112 inconsistent. Here we document a few of them.
 113
 114 .IP \[bu]
 115 2 Odds_XML.dtd
 116
 117 The <Notes> elements here are supposed to be associated with a set of
 118 <Game> elements, but since the pair
 119 (<Notes>...</Notes><Game>...</Game>) can appear zero or more times,
 120 this leads to ambiguity in parsing. We therefore ignore the notes
 121 entirely (although a hack is employed to facilitate parsing).
 122
 123 .IP \[bu]
 124 weatherxml.dtd
 125
 126 There appear to be two types of weather documents; the first has
 127 <listing> contained within <forecast> and the second has <forecast>
 128 contained within <listing>. While it would be possible to parse both,
 129 it would greatly complicate things. The first form is more common, so
 130 that's all we support for now.
 131
 132 .SH OPTIONS
 133
 134 .IP \fB\-\-backend\fR,\ \fB\-b\fR
 135 The RDBMS backend to use. Valid choices are \fISqlite\fR and
 136 \fIPostgres\fR. Capitalization is important, sorry.
 137
 138 Default: Sqlite
 139
 140 .IP \fB\-\-connection-string\fR,\ \fB\-c\fR
 141 The connection string used for connecting to the database backend
 142 given by the \fB\-\-backend\fR option. The default is appropriate for
 143 the \fISqlite\fR backend.
 144
 145 Default: \(dq:memory:\(dq
 146
 147 .IP \fB\-\-log-file\fR
 148 If you specify a file here, logs will be written to it (possibly in
 149 addition to syslog). Can be either a relative or absolute path. It
 150 will not be auto-rotated; use something like logrotate for that.
 151
 152 Default: none
 153
 154 .IP \fB\-\-log-level\fR
 155 How verbose should the logs be? We log notifications at three levels:
 156 INFO, WARN, and ERROR. Specify the \(dqmost boring\(dq level of
 157 notifications you would like to receive (in all-caps); more
 158 interesting notifications will be logged as well.
 159
 160 Default: INFO
 161
 162 .IP \fB\-\-remove\fR,\ \fB\-r\fR
 163 Remove successfully processed files. If you enable this, you can see
 164 at a glance which XML files are not being processed, because they're
 165 all that should be left.
 166
 167 Default: disabled
 168
 169 .IP \fB\-\-syslog\fR,\ \fB\-s\fR
 170 Enable logging to syslog. On Windows this will attempt to communicate
 171 (over UDP) with a syslog daemon on localhost, which will most likely
 172 not work.
 173
 174 Default: disabled
 175
 176 .SH CONFIGURATION FILE
 177 .P
 178 Any of the command-line options mentioned above can be specified in a
 179 configuration file instead. We first look for \(dqhtsn-importrc\(dq in
 180 the system configuration directory. We then look for a file named
 181 \(dq.htsn-importrc\(dq in the user's home directory. The latter will
 182 override the former.
 183 .P
 184 The user's home directory is simply $HOME on Unix; on Windows it's
 185 wherever %APPDATA% points. The system configuration directory is
 186 determined by Cabal; the \(dqsysconfdir\(dq parameter during the
 187 \(dqconfigure\(dq step is used.
 188 .P
 189 The file's syntax is given by examples in the htsn-importrc.example file
 190 (included with \fBhtsn-import\fR).
 191 .P
 192 Options specified on the command-line override those in either
 193 configuration file.
 194
 195 .SH EXAMPLES
 196 .IP \[bu] 2
 197 Import newsxml.xml into a preexisting sqlite database named \(dqfoo.sqlite3\(dq:
 198
 199 .nf
 200 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 201 .I "              test/xml/newsxml.xml"
 202 Successfully imported test/xml/newsxml.xml.
 203 Imported 1 document(s) total.
 204 .fi
 205 .IP \[bu]
 206 Repeat the previous example, but delete newsxml.xml afterwards:
 207
 208 .nf
 209 .I $ htsn-import --connection-string='foo.sqlite3' \\\\
 210 .I "              --remove test/xml/newsxml.xml"
 211 Successfully imported test/xml/newsxml.xml.
 212 Imported 1 document(s) total.
 213 Removed processed file test/xml/newsxml.xml.
 214 .fi
 215 .IP \[bu]
 216 Use a Postgres database instead of the default Sqlite. This assumes
 217 that you have a database named \(dqhtsn\(dq accessible to user
 218 \(dqpostgres\(dq locally:
 219
 220 .nf
 221 .I $ htsn-import --connection-string='dbname=htsn user=postgres' \\\\
 222 .I "              --backend=Postgres test/xml/newsxml.xml"
 223 Successfully imported test/xml/newsxml.xml.
 224 Imported 1 document(s) total.
 225 .fi
 226
 227 .SH BUGS
 228
 229 .P
 230 Send bugs to michael@orlitzky.com.