The user can enter different search conditions in the search panel, which is located on the left side of the main page (see Figure 2) and the second page (see Figure 3). The easiest way to enter search conditions is to use the free text search. Within the free text search you can enter a text string, which are being compared to the contents of the following fields of the data sets in the metadata catalogue:

• Name/Title
• Abstract/Description
• Keywords?

Free text search is available either on the first page (see 2 in Figure 2) or in the “Search” menu (Figure 8). If the user enters “soil” in the free text search field (2 in Figure 2 or 1 in Figure 8), for instance, and triggers the search by pressing the “Search” button (2 in Figure 2 or 8 in Figure 8, respectively), the system founds all data sets, which contain the word “soil” in the fields listed above. If more than one terms are entered, it will be interpreted as an “AND request”, meaning that the metadata-set must contain all of the search terms.

1. Free Text Search
2. What Filters
3. Where Filters
4. When Filter

Clicking on the “+” icon beside the “What ?” button(2 in Figure 8) opens a drop-down menu with sub-menus, which allow the user to define advanced search items icon namely “Topic Category”, “Sensor Type” and “Parameter”. These options are mainly of relevance for the search to sensor data.

The International Organization for Standards (ISO) metadata standard (ISO 19115) provides a set of Core metadata elements that must occur in every national profile/implementation. Most of these elements either map to existing CSDGM metadata elements or represent properties of the data that can be determined and populated using a data integrated metadata tool. Topic Category is the only mandatory element of the ISO core metadata set that requires new information that cannot be directly captured from the data. The domain for the Topic Category elements is defined by 19 subject headings. Clicking on the “+” icon beside the “Topic Category” item opens a list box with possible category names. Select one Topic Category of interest by clicking one of the entries in the list box. More than one category can be selected by clicking on an entry with the “Ctrl”-key pressed (e.g. “economy” and “biota”). Please note that within the category fields an OR relationship among the search terms will be used (instead of AND between the different search items). That means, that a search with more than one category selected will results in a larger number of results overview list, since the metadata must only contain one of the entered search terms.

The sensor type defines general categories of different sensors and is usually connected with the measured parameters. Querying data according to sensor types is identical to the topic categories (see section above). Clicking on the “+” icon beside the “Sensor Type” item opens a list box with possible sensor types. Select one item of interest by clicking one of the entries in the list box. More than one type can be selected by clicking on an entry with the “Ctrl”-key pressed. Like for the topic categories an OR relationship among the selected sensor types will be used (instead of AND between the different search items).

Clicking on the “+” icon beside the “Parameter” item opens an interface, which allows a user to query the data according to specific parameters (see Figure 10). The upper part of the interface contains a drop-down

Four items belong to the “Where ?” field (3), which are opened, when the user clicks on the “+” icon beside the “Where ?” field: “Metadata Fields”, “Catalogue”, “Regions” and “Spatial Search (Map extend)”. Click them to specify filter criteria related to locations (spatial as well as catalogues).

In the “Metadata” field (3) the user can specify, which fields of metadata sets will be queried during data search. By default, the items “Abstract” and “Title” are predefined, which means, that only these two fields are queried. Add additional fields for more extended queries.

The “Catalogue” field (4) allows to select the meta data catalogues to be queried1. All catalogues known to the system are shown here. By default, the “WASCAL Catalogue” is selected.

Here you can select countries from drop down list. If a region is selected, then a spatial search with a polygonal filter of boundaries of this country is performed.

If this check box is activated, then a spatial search with a bounding box filter with size of the actual map extend (google map on the right) is performed

By the “When ?” filter you can restrict the query to a specify time period. portal filter criteria. First check box 1 in order to enable the fields “From” and “To” to be entered. Select dates of your interest from the drop-down date picker. After initiating the search process by clicking the Search button the system searches metadata sets describing data within the specified period