meaning of dependency score?

["Jason Dunsmore" <jasondunsmore@gmail.com>]

What does "Score is -19" mean in this context? ...


# aptitude dist-upgrade
Reading package lists... Done
Building dependency tree... Done
Initializing package states... Done
Reading task descriptions... Done
Building tag database... Done
The following packages are BROKEN:
 php4 php4-mysql php4-sqlite
The following NEW packages will be automatically installed:
 libapache2-mod-php5 libconfig-file-perl mediawiki1.7 php5
The following packages will be automatically REMOVED:
 libapache2-mod-php4 libconfigfile-perl
The following NEW packages will be installed:
 libapache2-mod-php5 libconfig-file-perl mediawiki1.7 php5
The following packages will be REMOVED:
 libapache2-mod-php4 libconfigfile-perl
The following packages will be upgraded:
 apt-file mediawiki
2 packages upgraded, 4 newly installed, 2 to remove and 0 not upgraded.
Need to get 5636kB of archives. After unpacking 7328kB will be used.
The following packages have unmet dependencies:
 php4-sqlite: Depends: phpapi-20050606 which is a virtual package.
 php4: Depends: libapache2-mod-php4 (>= 4:4.4.4-3) but it is not installable or
                libapache-mod-php4 (>= 4:4.4.4-3) but it is not installable or
                php4-cgi (>= 4:4.4.4-3) but it is not installable
 php4-mysql: Depends: phpapi-20050606 which is a virtual package.
Resolving dependencies...
The following actions will resolve these dependencies:

Install the following packages:
libapache-mod-php4 [4:4.4.4-3 (testing)]

Score is -19

Accept this solution? [Y/n/q/?]