The theme element has the following definition:

<!ELEMENT theme (jdbc_query | jdbc_image_query | jdbc_georaster_query
| jdbc_network_query | jdbc_topology_query | map_tile_theme)?,
operations? >
<!ATTLIST theme
  name CDATA #REQUIRED
  datasource CDATA #IMPLIED
  template_theme CDATA #IMPLIED
  max_scale CDATA #IMPLIED
  min_scale CDATA #IMPLIED
  label_max_scale CDATA #IMPLIED
  label_min_scale CDATA #IMPLIED
  label_always_on (TRUE|FALSE) "FALSE"
  fast_unpickle (TRUE|FALSE) "TRUE"
  mode CDATA #IMPLIED
  min_dist CDATA #IMPLIED
  fixed_svglabel (TRUE|FALSE) "FALSE"
  visible_in_svg (TRUE|FALSE) "TRUE"
  selectable_in_svg (TRUE|FALSE) "FALSE"
  part_of_basemap (TRUE|FALSE) "FALSE"
  simplify_shapes (TRUE|FALSE) "TRUE"
  transparency CDATA #IMPLIED
  minimum_pixels CDATA #IMPLIED
  onclick CDATA #IMPLIED
  onmousemove CDATA #IMPLIED
  onmouseover CDATA #IMPLIED
  onmouseout CDATA #IMPLIED
  workspace_name CDATA #IMPLIED
  workspace_savepoint CDATA #IMPLIED
  workspace_date CDATA #IMPLIED
  workspace_date_format CDATA #IMPLIED
  fetch_size CDATA #IMPLIED
  timeout CDATA #IMPLIED
>

The <theme> element lets you specify a predefined or dynamically defined theme.

• For a predefined theme, whose definition is already stored in your USER_SDO_THEMES view, only the theme name is required.
• For a dynamically defined theme, you must provide the information in one of the following elements: <jdbc_query> (described in Section 3.1.2.9), <jdbc_image_query> (described in jdbc_image_query Element), <jdbc_georaster_query> (described in GeoRaster Themes), <jdbc_network_query> (described in Network Themes), or <jdbc_topology_query> (described in Topology Themes).
• For a GeoRaster theme, you can define some image processing options (described in operation Element).

The name attribute identifies the theme name. For a predefined theme, the name must match a value in the NAME column of the USER_SDO_THEMES view. For a dynamically defined theme, this is just a temporary name for referencing the jdbc_query-based theme.

datasource is an optional attribute that specifies a data source for the theme. If you do not specify this attribute, the data source for the map request is assumed (see the datasource attribute explanation in map_request Attributes). By specifying different data sources for different themes, you can use multiple data sources in a map request.

template_theme is an optional attribute that can be used to render two or more themes when a predefined theme has same name in multiple data sources. You cannot repeat theme names in a map request, but if you have two different data sources with same predefined theme name, you can use this attribute to render both themes.

The following example specifies two themes that are based on a US_STATES theme that exists in two data sources, but that has a different content in each data source.

<themes>
    <theme name="US_STATES"
           datasource="dsrc" />
    <theme name="OTHER_US_STATES"
           template_theme="US_STATES"
           datasource="other_dsrc" />
</themes>

The max_scale and min_scale attributes affect the visibility of this theme. If max_scale and min_scale are omitted, the theme is always rendered, regardless of the map scale. (See Map Size and Scale for an explanation of max_scale and min_scale.)

The label_max_scale and label_min_scale attributes affect the visibility of feature labels of this theme. If label_max_scale and label_min_scale are omitted, the theme feature labels are always rendered when the map scale is within the visible range of theme scales (that is, within the max_scale and min_scale range). (See Map Size and Scale for an explanation of label_max_scale and label_min_scale.)

label_always_on is an optional attribute. If it is set to TRUE, MapViewer labels all features of the theme even if two or more labels will overlap in the display. (MapViewer always tries to avoid overlapping labels.) If label_always_on is FALSE (the default), when it is impossible to avoid overlapping labels, MapViewer disables the display of one or more labels so that no overlapping occurs.The label_always_on attribute can also be specified for a map feature (geoFeature element, described in geoFeature Element), thus allowing you to control which features will have their labels displayed if label_always_on is FALSE for a theme and if overlapping labels cannot be avoided.

fast_unpickle is an optional attribute. If it is TRUE (the default), MapViewer uses its own fast unpickling (unstreaming) algorithm instead of the generic JDBC conversion algorithm to convert SDO_GEOMETRY objects fetched from the database into a Java object accessible to MapViewer. This process improves performance, but occasionally the coordinates may lose some precision (around 0.00000005), which can be significant in applications where all precision digits of each coordinate must be kept. If fast_unpickle is set to FALSE, MapViewer uses the generic JDBC conversion algorithm. This process is slower than MapViewer's fast unpickling process, but there is never any loss of precision.

mode is an optional attribute. For a topology theme, you can specify mode="debug" to display edges, nodes, and faces, as explained in Topology Themes. The mode attribute is ignored for other types of themes.

min_dist is an optional attribute. It specifies the minimum on-screen distance (number of pixels) between two adjacent shape points on a line string or polygon for rendering of separate shape points. If the on-screen distance between two adjacent shape points is less than the min_dist value, only one shape point is rendered. The default value is 0.5. You can specify higher values to reduce the number of shape points rendered on an SVG map, and thus reduce the size of the resulting SVG file. You can specify different values in different theme definitions, to allow for customized levels of detail in SVG maps.

fixed_svglabel is an optional attribute that specifies whether to display the labels on an SVG map using the original "fixed" labels, but having them appear larger or smaller as the zoom level increases (zoomin) or decreases (zoomout), or to use different labels with the same text but different actual sizes so that the apparent size of each label remains the same at all zoom levels. If the fixed_svglabel value is specified as TRUE, the same theme labels are displayed on the map at all zoom levels, with the labels zoomed in and out as the map is zoomed in and out. If the value is FALSE (the default), different theme labels are displayed at different zoom levels so that the size of each displayed label appears not to change during zoomin and zoomout operations.

visible_in_svg is an optional attribute that specifies whether or not to display the theme on an SVG map. If its value is TRUE (the default), the theme is displayed; if it is set to FALSE, the theme is not displayed. However, even if this attribute is set to FALSE, the theme is still rendered to the SVG map: the theme is initially invisible, but you can make it visible later by calling the JavaScript function showTheme() defined in the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

selectable_in_svg is an optional attribute that specifies whether or not the theme is selectable on an SVG map. The default is FALSE; that is, the theme is not selectable on an SVG map. If this attribute is set to TRUE and if theme feature selection is allowed, each feature of the theme displayed on the SVG map can be selected by clicking on it. If the feature is selected, its color is changed and its ID (its rowid by default) is recorded. You can get a list of the ID values of all selected features by calling the JavaScript function getSelectedIdList() defined in the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

part_of_basemap is an optional attribute. If the map format is SVG and the value of this attribute is TRUE, MapViewer renders the theme as part of and on top of the base map, which is rendered as a raster image.

simplify_shapes is an optional attribute that specifies whether or not the shapes are simplified before being rendered. Simplification is useful when you want a map display with less fine resolution than the original geometries. For example, if the display resolution cannot show the hundreds or thousands of turns in the course of a river or in a political boundary, better performance might result if the shapes were simplified to show only the major turns. The default is TRUE; that is, shapes are simplified before being rendered. If this attribute is set to FALSE, MapViewer attempts to render all vertices and line segments from the original geometries, and performance may be slower.

transparency is an optional parameter to define the basic alpha composing value to be applied on themes during rendering. The value can be from 0 to 1, with 0 meaning completely transparent and 1 (the default) meaning completely opaque (no transparency).

minimum_pixels is an optional parameter that defines the level of resolution to be used on the spatial filter query. This may be useful to avoid rendering too many elements at the same position of the screen. (See the Oracle Spatial and Graph documentation about the min_resolution and max_resolution options for the SDO_FILTER operator.) The unit for minimum_pixels is screen pixels. For example, minimum_pixels=1 means that the spatial filter query will not return features with a resolution less than the amount that 1 pixel represents for the current device window and current query window.

onclick is an optional attribute that specifies the name of the JavaScript function to be called when a user clicks on an SVG map and theme feature selection is allowed (see the selectable_in_svg attribute explanation). The JavaScript function must be defined in the HTML document that has the SVG map embedded. This function must accept only four parameters: the theme name, the key of the feature, and x and y, which specify the coordinates (in pixels) of the clicked point on the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

onmousemove is an optional attribute that specifies the name of the JavaScript function to be called when a user moves the mouse on top of any feature of the theme on an SVG map. The JavaScript function must be defined in the HTML document that has the SVG map embedded. This function must accept only four parameters: the theme name, the key of the feature, and x and y, which specify the coordinates (in pixels) of the point for the move on the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

onmouseover is an optional attribute that specifies the name of the JavaScript function to be called when a user moves the mouse into a feature of the theme on an SVG map. (Unlike the onmousemove function, which is called whenever the mouse moves inside the theme, the onmouseover function is called only once when the mouse moves from outside a feature of the theme to inside a feature of the theme.) The JavaScript function must be defined in the HTML document that has the SVG map embedded. This function must accept only four parameters: the theme name, the key of the feature, and x and y, which specify the coordinates (in pixels) of the point at which the mouse moves inside a feature on the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

onmouseout is an optional attribute that specifies the name of the JavaScript function to be called when a user moves the mouse out of a feature of the theme on an SVG map. The JavaScript function must be defined in the HTML document that has the SVG map embedded. This function must accept only four parameters: the theme name, the key of the feature, and x and y, which specify the coordinates (in pixels) of the point at which the mouse moves out of a feature on the SVG map. For information about using JavaScript functions with SVG maps, see Appendix B.

workspace_name, workspace_savepoint, workspace_date, and workspace_date_format are optional attributes related to support for Workspace Manager in Mapviewer, which is explained in Workspace Manager Support in the Map Visualization Component.

fetch_size is an optional attribute that specifies how many rows will be prefetched into memory. The default value is 100.

timeout is an optional attribute that specifies the number of milliseconds to wait for the connection to the WMS or WFS server.